Inconsistent Idle

[skhurst18]

I have a 87 Chevrolet Silverado with a 5.7L TBI. When I start the engine, it idles real low and tries to stall. If I increase the accelerator, it eventually smoothes out and runs fine. Once it warms up it idles high(no tachometer). When I put it into reverse or drive(automatic 700R4) it idles very low again and tries to stall. I have replaced the IAC, Positioning Sensor, and replaced all of the gaskets, o-rings, and filters in the throttle body. I replaced dual 16 gallon tanks with 20 gallon, with new sending units and pumps and fuel filter. I also removed the smog pump and system. This problem was occurring before I made all of these changes. Can anyone give me any suggestions? Thanks.