When driving my Van (302 EFI 5.0 Engine) between 30 to 40 mph the engine seems to studder (like a miss) after the 40 mph range has pass and I get up to 45 mph I have to let up on the gas a little for the overdrive to kickin, right before it does this, I hear a whisle sound from the engine compartment. The Transmission shifts hard while light accel. I have done the following to try to cure this:
Changed plugs and wires, gap to 45
Checked all vaccum hoses and replace those that were cracked or loose fitting.
Replaced the Vaccuum 3 way connector from the Brake Booster.
Replaced the Temp Sending Unit. (from top of engine)
Replaced the IAC.
Checked for codes from the computer, get none.
Disconnected the Battery to reboot the computer...still no codes.
All wires are good looking, no oil on engine or dirty.
The engine starts up fine.
No pinging or knocks.
Engine heads has been replaced/rebuilt from machine shop. Air pump missing or was there one to begin with?
Exhaust mantifolds doesn't have the air inlet tubes normally found on an EFI engine.
Oil pressure is a little high but drops down after warm up to middle of gage.
Anything else I missed?

 

The whisle sound could be a vacuum leak. Check the the area where the upper and lower manifold meet. On both my 5.0 trucks the gasket creeped out near cyl 1.

Also what trans? AOD? If it is, the hard shifting sounds like the TV cable. Unless it's really hard I'd leave it alone as it's better to be a little on the high side (which will cause hard shifts) then on the low side (Which will cook the trans...)

If it's too high for your tastes, any hanes or chiltons manual for the E/F series should tell you how to adjust it. It's not that hard.

 

AOD, going to check the book again...engine doesn't leak, clean as can eat off of....heads has been reworked, good compression, no smoke or bypass..when brought it, had the trans filter changed and the torque convertor fluid changed, no shaving in pan. but haven't checked the TV cable, no vaccum modultor on this model of trans.