when cold runs thru rpms like you where running a 1/4 mile no problems. when on 1990 Dodge D150

warm to proper running temp floods out about 2100 rpms when running down the street. you can feather the throttle when parked as high as you want with just a little hesitation.

Asked by for the 1990 Dodge D150
check the fuel pressure.
check the back pressure from the cat converter.
have the coolant sensor checked for proper operation

have replaced coolant sensor. cat was removed ran the same, checked cat out reinstalled ran the same, checked fuel pres. no problem there. fuel pump was replaced along with fuel filter and tank was cleaned out completely. has new plugs, cap, wires, and coil. replaced ecm too, also smog/air pump checked out. I happen to work for local parts store have asked several local mech no help. all I've learned is they don't know much more than I do.I don't know what else to do.