problem with a slight miss and other odd issues

[sdelmar]

Hello all! I am new to the forum, but I have read several threads over the last few months. It looks like there are a lot of knowledgeable people on here, so I thought I would join and get some advice!

I have a 95 Sierra K1500 350/4L60E. I recently put a GM crate motor in after sucking a valve at 400,000 miles (my fault, I presume, after letting it overheat while rushing to the hospital on a bad radiator). Anyway, it has a slight miss at idle that can also be noticed at constant speeds around town (lower RPM). It has new plugs and wires, distributor checked out well with no play in the shaft, new cap and rotor, coolant temp sensor is working well and I have no exhaust leaks...at least that can be heard over the engine. It also runs very sluggish when cold while in closed loop and occasionally hesitates, almost killing the engine, when I hammer the throttle from idle. I have been getting a "lean exhaust" code that comes and goes, but most commonly comes on when driving at a constant speed. O2 sensor is working, vacuum is strong and I have a new fuel pump and fuel filter. When I replaced the fuel pump apparently a hose was not attached well because fuel spills over on fill-ups. To the best of my knowledge I don't think this should cause a problem on a low pressure TBI setup, but I'm not sure of that.

I have not checked fuel pressure, but the injector spray seems to be strong. Things I have on my short list to check out are:

1)map sensor
2)fuel pressure
3)ignition module

Sorry about the lengthy post, but I wanted to make sure I included all the info I have. Thanks in advance for your help! I am getting frustrated with this problem that I continue to throw money at!!!