2001 Trooper runs rough after timing belt replacement
 

Hello. I will be extremely grateful if someone can solve my dilemma: I just replaced the timing belt on my 2001 Trooper and now it idles and runs rough, and pings and knocks. I was very careful to line up the belt marks and pulley marks (I even took pictures so I could reassure myself later just in case something like this happened). Is it possible for the the belt marks to off a tooth? (the belt is a Genuine Isuzu part). If I take the accessory-drive belt off and run the engine, it runs smoothly and revs fine (maybe a SLIGHT hesitation), so it's definitely affected by load. (With the belt on, if I turn the AC on, it almost won't run). Could the belt tensioner be the problem? (I didn't replace it - I did compress it in a vise for installation of the belt and it didn't expand when I removed it from the vise, I thought it would expand when the engine ran (which it did)). It sure doesn't seem like that would be the problem since it's on the slack side of the belt, but at this point, I'm looking at things like this.

If the belt marks are indeed off, how do you reset the cam timing? I see marks on the heads, but not sure what to line the crank pulley mark up to. (after typing this, I took everything off and took another look and the pulley marks line up perfectly with the engine marks - I found the crankshaft mark on the driver's side of the pulley - so the cam timing appears to be correct (I used the same paint marks on the pulleys that you use for the white stripes on the timing belt)

Thank you so much in advance for your help. I'm developing bald spots from scratching my head so much over this one.