Cold start 1988 5 liter cheyenne

[gerry lecky]

Recently my son and i removed his 1989 4.3 and installed a 5 L from a 1988 Chev cheyenne. Complete job was done (computer, wiring harness etc). The two issues we have with the trruck now are.

1. On cold start it starts ok but does not idle up much or for long and when driving before it fully warmed up it tends to bog out on acceleration. once temp is up to operating range it runs and perfroms perfectly!

2. When engine is either cold or up to operating temperature and the truck is backing up slight grades the truck bogs out and sometimes stalls when you let off the acc pedal. Almost acts the same as what it does cold in the forward gears. Transmission is strong and will spin wheels on asphalt in both forward and reverse gears.

any ideas?????????????