1988 Chevy Silverado intermitent miss/ poor performance

Ok.I just bought a 1988 chevy half ton four wheel drive single cab long box. It has a 5.7/350 in it out of a 1987 with 50k miles on it. When I bought the truck it was extremely out of time, I re-timed it with a timing light.
it starts really cold like a carbureted motor would. It is throttle body injected. When driving down the road it has a slight miss, but when it is warm the check engine light comes on and it wants to stall when trying to hold a speed. When accelerating rapidly it acts somewhat fine. I have replaced the fuel pump, O2 sensor, temp sending unit and sensor, fuel filter, cleaned injectors, new cap rotor and coil, plugs and wires.