Sounds interesting!
What's TP going to be called in your game? Is there a particular storyline reason why you decided that gaining TP and going over a certain number would paralyze the characters, as opposed to losing TP and falling below a certain number?
There's nothing inherently wrong mechanics-wise with that decision, but without an explanation of what TP or the TP gauge are supposed to represent in your game it could be counter-intuitive or confusing for some players. "Gaining" something tends to sound more positive, and "losing" something tends to sound more negative, but in your game it's reversed. If your TP meter were called a "Fatigue" or "Overload" gauge or something such that could help.
There are some similarities to what I'm doing with TP in my project: Most classes start with 100 TP (called Stamina Points or SP), and most actions (including normal attacks with equipped weapons) cost TP. If a unit's TP reaches 20 or below it enters a Fatigue state in which all their stats are halved, until they go over 20 TP again (they can still act but are terribly weak offensively and defensively). Different classes automatically recover TP per turn at different rates, such that different actions for each actions will result in a net decrease, increase or even break in TP for that turn. For example, a Human class unit may lose some TP each turn it performs a regular attacks with an equipped Ax, but a Zombie class unit using the same Ax normal attack may break even. The same rules apply to enemy troops. Skills that cost MP typically cost less TP, as well.
So with my TP system I've had to think through some issues common your TP system, and here's couple things to consider with yours:
1) Is losing 2 TP per turn (each time you attack or guard) the only way units can reduce the TP gauge?
In my project I tried to give different classes different ways in which they spend and regain TP, to effectively give them different "tempos" or play-styles. For example, Flying classes units are glass cannons that can take two actions per turn and doing two front-row attacks will have a high TP cost, but they also have a skill called Roost which recovers TP, the more the TP lost the higher the regain (but the skill costs their entire turn and reduces their Evasion to zero for that turn, making them rather vulnerable since their other defensive stats are low). So a Flying unit can be played in cycles of high burst damage followed by retreating/recovering TP. On the other hand, sturdy Insect class units have movesets that allow them to gradually buff their stats and the amount of TP they regain over time, such that they can use their more powerful skills more efficiently and freely as the battle progresses.
Some classes can recover TP by last-hitting enemy units, some by sacrificing their MP, some at the cost of temporarily debuffing some of their own stats, some support units can transfer their own TP to ally units, etc.
So in your project would there be any other options to reduce TP other than to attack or guard (or use low TP-gain magic)? Is there any way to reduce more than 2 TP at a time?
2) Is paralysis the best penalty for going over 40 TP?
How much do skills cost in your game? If they raise the TP bar by like 3-5 TP on average, then that's a lot of actions/turns before a character can reach 40 TP. But if skills cost like 6 to 10 TP on average, that means an action could paralyze a player for like 3-5 turns. Not very fun, and especially frustrating on a misclick.
In my particular project I briefly thought of paralysis being the penalty for hitting 20 TP or below, but went I with stats being halved for a variety of reasons. Paralysis is unfun and would probably make worse the biggest risk of my TP system--the player getting "stuck" in a situation where they'll always have low TP unless the battle drags on and on. That's a real drag and invites the player resetting the game in frustration. To avoid this, since different units have actions that can recover TP, I wanted to at least give those units the chance to use them to get out of their situation, rather than make the whole system only a matter of prevention. The stat halving also makes it so that if a player just unwisely spends all their TP on all their characters at the same time, the enemy troop would likely just wipe out the party and end the battle. The player would be back playing again in a jiffy, ready to try a different strategy with their full options available to them.
I'm not saying that you should do what I did in my case, since we do have some notably different rules, but I do think it's good to consider what will happen when TP get too high and what the player's experience will be like. Some players may spend a lot of TP because it seemed like it would be enough to end the battle, but if it turns out to not be a case through no fault of their own they could be in for a drag. Misclicks do happen, and paralysis for several turns, followed by no skills for several more turns, could be a real pain.
One simple thing that I think could help your current system a lot without changing too much is if one character is currently paralyzed due to going over 40 TP, other characters could sacrifice their turn (and gain 2 TP) to reduce the paralyzed character's TP gauge. This could help the going over 40 TP rule still feel like a penalty (other characters have to sacrifice their turns) without it being as much of a dead end or black hole.
You could maybe also play around with having characters being able to do this at any time (not just when the target character is paralyzed due to going over 40 TP). For example, perhaps one character has a skill that halves magic damage for the entire party and you're up against a boss that uses a devastating magic attack after a one turn warm-up, but if the character used the anti-magic shield every time it's useful they would gain TP too quickly. So the player could pull off a neat strategy by having several characters sacrifice their turns to fund the use of the anti-magic shield as much as needed.