94 T/a, stock except for k&n cai , happens from just off idle till about 3k rpms with under 1/2 any thing more than half throttle it takes off like normal. the engine is rebuilt and everything is new with the exception of maf, icm and injectors. Had the computer scanned and nothing can up and the mechanic (my boss) said everything is running where it should be. the fuel pressure is good ( new fp) every sensor checks out good . just put new acdelco plat. plugs in gaped at manufacture specs. I noticed when i start it up in the morning and look at the engine its not shaking, but when its warm it has a bit of a stumble. i pulled each injectors connector and it lugs down the engine like it should, some more than others though. my boss did say that the battery and so is the positive cables(gets hot) the battery stays at a constant 13 volts except for when the lights are on and it will go down to about 12.
im stumped on this one, could a failing battery/altenator be the cause of this?

 

Since you have no responses yet, I'll take a shot at this...

Have your ignition scoped. It will tell you if the ignition system has a problem, and exactly where it is. I think your battery voltage is OK.