If you're feeling up to it, here is a guide on setting up your distributor correctly:
Distributor Replacement

 

That's a good guide but keep in mind: When both marks on the dampener are lined up like this:




#1 cylinder is at TDC, but there's no guarantee that its on its compression stroke. It could be at TDC of the exhaust stroke. It takes two complete crankshaft revolutions, (720 degrees) for all cylinders to complete each of their 4 cycles, (intake, compression, power, exhaust). If the distributor is installed on the incorrect cycle, P1345 will set and the engine might not start, but if it does, it will backfire through the exhaust, or intake, or both. Basically you have a 50/50 chance of installing the distributor correctly, even when following this guide. In most cases it's easier to just pull the distributor out, rotate it 180 degrees and reinstall it.

 

Sounds to me likes its 02 related. I agree with Burned first post.

Check your 02 sensors, make sure they are all plugged in. I suspect your puter is operating in OPEN mode. In open mode the puter disables emissions systems until the engine is at proper operating temperature. It will perform as usual, however the key indicator is your fuel economy will suck. Once the puter recognizes proper engine tempurature (based on the 02) it enables all emission systems and controls engine operation accordingly. You could be in open mode and never trip a CEL, especially on older vehciles.

Click below for a tech article on how GM 02 sensors operate.
o2-sensor-testing