[Bill j]

truck runs great in town, open it up on highway and it looses power, rpm drops off, No service engine lamp, no codes. any ideas, thanks

 

[mopar56]

Hi welcome to the forum, these motors were known for intake leaks when you open up the throttle the vacuum changes which could effect horsepower do you have any oil consumption issues as well, (a good sign of intake leak), another issue could be a baffle in the exhaust, the more pressure in the system the more the loose baffle gets pressed against the exit blocking flow and loosing power

 

[chuzz]

Tap your catalytic converter with a rubber mallet or something and see if you hear rattling coming from inside it. It may be stopped up.

 

[Bill j]

Ended up being the muffler, thanks for the help