Have a 2002 ford f-150 rwd with a 5.4 triton.

every time I take it to the garage it stops. Here is the issue

On really hot days even if I don't run the AC in when i have to sit and idle it will start dropping to a low idle and even if I put my foot on the brake it will try to lurch forward in self drive but If I am right behind someone and I can't take the foot off the brake at all it might stall all together or take off but have no power then a few seconds later the gas will work again. Because of it not doing it all the time though I have not been able to pinpoint the exact issue I thought it was a faulty gas cap and maybe rain got in the gas but I put a new cap on and it was fine after that until today. I also noticed every now and then I need to unhook my battery cables so the gas cap light will go off in the dashboard if not it will stay on. I am not a mechanic so it really is hard for me to explain the issues but maybe with more interaction I can narrow it done more.

 

I think I narrowed it down to spark plugs or thermostat but i am leaning towards the plugs. The only issue is the truck seems fine until it gets high 80's or 90's out. I took my wife to work this morning though when it was 65 out and truck had no issues at all.

 

Plugs would be a good place to start. Is your truck overheating or not coming to full operating temp at all?