Is it possibly for a car to lose hp because of an abundance of electronics hooked up to the battery?

I have a 91 rx7 fc that has just one battery and I have a different fan from the factory one, that is hooked straight up to the battery and i also have a subwoofer that's amplifier is hooked up to the battery as well. I'm curious if it's possible that my car is slower just because I have these things drawing amps from the battery while it's running

i can move my stick from drive to neutral without touching the break?

Should i be worried about this? It only does it for drive to neutral and neutral to drive. I just discovered it does this today and it scared me because i already got a brand new transmission in my car, and didnt want to pay another 5 grand to get it fixed. Btw, its an envoy xl, not sure the year, but i think around '09. Its relatively new, and only has three problems. The door panels need replacing, the thing i mentioned with the clutch, and the gas meter goes up the faster i drive. All three i feel are easily fixed, but the clutch is the thing that frightens me the most. When it did it (when i accidentally punched in in neutral while driving) it didnt make a noise other then the engine. I had a problem with the transmission before where it couldnt reverse, though i tested multiple times, and it seems fine. No noise, no problem switching gears, nothing, just thay i can change gear without touching the break, or the button on the clutch (excuse me, im not good with cars parts, so idk what its called, and if i used "clutch" wrong, i apologize)

This may be a solution. I had this problem once too, and i felt like such an idiot when i figured it out. If you can at least turn it on (not started, just on. It wont drive, but you can still use the radio and stuff), then check if its in parked or not. I had the problem and almost broke the key cause i couldnt get it out, and couldnt turn it. Then i realized it wasnt in park.

Just check first, then call a mechanic if it still doesnt work. Hope it helps!

First problem was you replaced the thermostat for no reason nor was it the reason it was causing the problems your having. Not sure why people always blame the thermostat when its very rarely to ever stick close, it always sticks open & causes a no heat condition during the winter.

I would first look at the reservoir/radiator cap & see if it holds pressure or just replace it with a good GM part.

The auto parts stores also make kits where you can check for head gasket issues, try one.

The other issue may be your transmission either low on fluid or about to go south.