I recently replaced my Iac and fuel pump in my 1997 Ford F150 4.6L
and now I have noticed it's not shifting. When accelerating up to 45 mph
the trucks rpms remain at 2000.
Now most times when I let off the gas the truck will shift
and the rpms will drop. Like I said this problem has recently shown
itself just after replacing my IAC and replacing my fuel
pump. I don't think the fuel pump has anything to do
with this, but I am worried that the aftermarket
IAC may be the problem, however the transmission
could also be an issue. Any help would be appreciated.

 

Have you checked your throttle position sensor voltages?

D

 

Agreed, but to add additional things to check.

Is the transmission oil level correct?
You may need to remove the throttle body housing and give it a complete cleaning, as there are 2 EGR internal ports, which if plugged, may contribute to the issue. While that is off it is easier to clean the back side throttle plate too.

The aftermarket IAC may not be playing well either and contributing to the problem.

and check for vacuum leaks