95' Trooper won't start all the time

It all started 5 months ago. I came out of the store, turned the key and nothing. I didn't even get a click from the starter trying to turn over. So, I call AAA for a tow and wait. While I wait I tried numerous times to turn the engine over, and wait some more. Finally, On one last try it starts. The next day the truck starts fine all day, that night I changed the spark plug wires(Old wires were in need of replacing). When I finished I went to start the truck and nothing. Now I decide to take the starter out and have it tested. The starter was good ( I should mention I put this starter in about 1.5 years ago) better than the one they had on the shelf. Take it back home and put it in, the truck starts and has ever since two weeks ago. Same thing almost, I used the truck as normal stopped at a friends house went to start the truck and nothing. THIS IS WHERE IT GETS STRANGE. I turn the key over a few times and I'm not even getting instrument warning lights( supposed to come on and go away every time you turn key). About 10 minutes later the l warning lights are coming on, 5 minutes after that the engine turns over but will not start. I had AAA tow me home and the next morning the truck starts. So, I took it to my machanic, they were unable to diagnose because the truck had started and reset all the codes in the computer. Two problems they guessed at, Throttle body had excessive carbon build up(I had them clean it), Fuel Pressure Regulator might have a leak but wasn't leaking at that time(I did not have it replaced). For the next 5 days the truck starts fine. Use the truck like normal untill the evening and we're back at it. Won't start, this time if you turn the key the engine does nothing, but all the instrument panal and dome lights fade as you turn the key. So, I call AAA they jumped it and it started, I went right to the store and bought a Dihard battery. The truck starts fine for a day, then it decides that every so often it wants you to turn the key about 10-15 rapidly untill it wants to fire up. On the 4th day in the eve. that trick doesn't work anymore. AAA comes out (same guy 3 times in a row) we try and turn the key nothing, we try putting it in nuetral and turning the key nothing(only the instument lights come on). Then we crawl underneath so, I can show him that the starter wires are not corroded. I pulled off the slip connecter, it was clean, put it back on. Crawl out from underneath and turn the key it starts. It has been 1 day since that and it has started numerous times. Someone with some advice or knowledge of this problem please help, it's only a matter of time before it won't start again.

The most likely fault is the ignition switch not the key switch the switch behind the key switch a common problem throttle bodies ect are a waste of money the fault is definetly electrical not engine management

Find another mechanic! Sounds like they are more interested in what they can profit on (Two problems they guessed at, Throttle body had excessive carbon build up(I had them clean it), than trying to help you. The last responder, beauford, was right, it is not an engine management problem!

I agree with beauford sounds like ignition switch

Do you have to press in the clutch to start your truck even if it is in neutral? If so, check that switch.

I had some phantom problems like these as well. The only way I seemed to get rid of them is selling the truck ; )