1999 Chevy Suburban poor idle and driveability

Chevy Suburban K2500 7.4L 454 Big Block. Hey i just did a top end rebuild, including fuel injectors, heads rebuilt, alternator, waterpump, starter, repaired all vacuum leaks, plugs, wires, cam shaft position sensor, cap and rotor, New gaskets every where. I suspected the O2 sensors and replaced them as well. My problem is it takes several engine rotations to start and when it does it hesitates at idle (750 rpm) and shakes and shutters even at running temperature (195 degrese F). At a stop light idle is 750 but when i accelerate it studers until i hit 30mph or 2000 rpm and runs smoother. My scanner says no DTC and the manifold absolute pressure is 10.5 mercury and should be at 28. Also with my foot on the brake and put it in drive the idle drops below 500rpm and nearly stalls (automatic trans). the scanner says my throtle positon sensor is reading correctly. My Long term fuel trim and short term fuel trims are ranging from -50.0 to -20.0 even with the new oxygen sensors no where near the recomended 0.0. Runs realy rich... spark is advanced 25 degrees by the computer, i reset the timing manualy and hit it with my timing light. the spark advance stayed at 0 for about half a second and advanced to 25 ATDC. droped in the distributor at spec 4 degrese BTDC.

Help me two car pros!!