no more then 1800 rpms while driveing on 1990 Ford F-250

while driving will not exceedd 1800 rpms timing o k carb adusted correctly has fuel reg. set @ 3. 5 #

Asked by for the 1990 Ford F-250
Have you checked for possible exhaust back pressure probs or trans probs?
exhaust good 4spd trans sitting in nuetral only go
1500 to 1800 Rome only
Does have a fuel reg. Based on
Weber carbs suggestion