Isuzu Forums - Isuzu Enthusiasts Forum - help!! Amigo misfire, no check engine light

Howdy Isuzu'ers I recently bought a 2000 Amigo 3.2L V6 2wd with 110k miles on it. It has a intermittent misfire issue since I first bought with no check engine light ever coming on. I thought It may be fixed with a good tune up but still has misfire issues. The engine also takes a long time to start up and when it does there is a initial squeak in the alternator belt and the highlights dim in and out only initially then goes to normal after some driving. So here is a list of all I've done.I also notice the misfires also happen right after hitting bumps on the road or on a long turn.

-New Duralast battery
-Replaced old autolight double platinum spark plugs with bosch iridum (Afterwards I read on another forum that this type of engine only runs properly with ngk or denso copper spark plugs which I have ordered and will replace again, could this be the whole issue?)
-Replace air filter with a K&N
-Replace fuel filter with a Fram
-Replace PCV valve with a Fram
-Replace throttle body with another used one(Dad's mechanic shop said it was the only thing they could find that was not working properly, it still misfires but not as much, now it seems to have occasional stalls)
-Replaced timing belt and water pump, just because I have no idea if it's ever been done and didn't want those going bad on me.
-Replaced serpentine belt with a goodyear gator back ( belt still squeaks initially and seems to have a bit of slack which I figure the auto tensioner is going bad which I have ordered, hope it takes care of the initial squeak and head light initial dimming)

The only other thing I can think of is a bad fuel pump. Does anyone know if that could be causing the misfire with no check engine light? I'll see what the new spark plugs do before going that route. Any other ideas?? Thanks.