Installed new distributor need help

I installed a new distributor in my 88 Suburban (5.7). I followed the installation procedure (TDC, point roter to #1, etc.) I timed it (I think it's adavnced about 10-12 degrees) and generally speaking, it runs great. However, during cold starts (overnight or several hours) it snorts and jumps and backfires until it warms up a bit and then everything runs smooth. I replaced the coolant sensor and checked for vacum leaks, etc. Everything appears OK. It all started when I replaced the distributor. What the heck did I do wrong? Would being one or two teeth off with the distributor be a problem if it times OK? Help please.

did you unplug the timing advance connector when you set the timing if not it's probably over advancing

did you unplug the timing advance connector when you set the timing if not it's probably over advancing

No I didn't. Where is that located? So I unplug the advance connector, time as usual and then plug it back in?

it's single wire connector i think it's by the left side of the firewall. follow the distributer wires and you should be able to find it.

I think it is a tan/black wire inside, just under the heater box, above where the passanger's feet go (I coild be wrong). Should be set at 0 deg.