I am betting your mileage improved a lot as well. The other thing I was going to suggest was setting the IAC but the temp sensor fixed it, they die often.
I had that drain back issue on my 94 Z71, a new fuel pump fixed it. I would also reset the IAC, if the their isn't enough air, it can act like that. What RPM does it idle at? I ground the tamper plug and turned mine up.
I had a feeling it may be a fuel pressure issue. I will have to check it out tomorrow when it is light out. I don't remember seeing any relays in the fuse panel. Would they be someplace different? Also I did change the fuel filter this morning after the car sat all night. There wasn't any fuel in the lines at all.... I was expecting some but none came out.
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