Stumble on Acceleration

[Cstray]

Just installed a 5.7 350 tbi into my 1990 k1500. It idles smooth. At 1500 rmp is smooth. But accelerating from idle it stumbles. Once I'm at 1500 or so rmp no issues in acceleration. During driving only stumbles from a dead stop. No issue at speed. Timing is set at 0 degrees TDC.

 

[Schurkey]

"RMP"? Royal Mounted Police?

What is the fuel pressure?

How old are the usual 'tune-up" items--cap, rotor, plug wires, plugs, fuel filter, air filter, PCV inspection, EGR inspection, etc?

Connect a scan tool, look at the data stream. Verify ALL the sensors, especially TPS, and MAP. Find out what the computer wants you to know.