93 rodeo engine power loss

couldnt find this in other discussions.
my 93 which now has 95 passport motor with 117k miles and is 3.2 after driving for about 45 min or so... losses power spits and sputters and backfires and if you turn the motor off even while driving it shuts off and you restart it takes of like nothing was ever wrong. any ideas about what this could be would be greatly appreciated. I had a bad cylinder and replaced the motor. was kinda having this problem before engine change only parts that we transfered were the intake and coil packs... put other coil packs on and it still did it so thats probably not it. thanx in advance.

engine coolant temp sensor? i know it sounds weird but it could be the problem, mine does it too, well something like that and i plan to fix it today?