[Smokey71]

I can floor the pedal of the mustang and top speed gets up to almost 45mph. I have changed spark plugs, wireset, distributor and rotor button. When going uphill the car has to be downshifted to about 2nd gear. With the pedal still floored it almost just quits moving. These are not steep hills. Just standard hills down the highway. Any other suggestions of what this might be.

[Stangmansteve]

well a sarcastic answer would be...go get a 5.0 and problem solved...

but how about something practical

1. there might be a compression ratio problem.
2. there might be a fuel issue.
3. check the air filter
4. check the ECU

[Dana W]

Does your throttle butterfly open all the way up? Check the linkage.

[TOM RENZO]

CLOGGED CAT MAYBE????????????????????? Did you check it.

[johnny2350]

Check the exhaust system, the cat or muffler could be shot. if u want a replacement try www.rockauto.com. I know cuz it just happend to my friends 1990 and thats how we fixed the problem.

[pookie_25_52]

could the Throttle positioning sensor be out of wack?

[Smokey71]

I checked a little deeper and do think there is back pressure coming up from the cats. Having them cut out and replaced with straight pipe. If that doesn't clear it up. I am going to try your other suggestions. Will post again after the pipe replacement to let you know. Thanks for the input.

[Smokey71]

Major difference. Unclogged the first cat and removed the second one. Now I can get it up to speed. Do have a slight erratic idle issue but going to replace the TPS and the IAC Valve and hope it helps. Thanks for all the input.