I recently got a good deal on a 03 3.9l manual
it’s a decently quick truck from 1-4 but as soon as you get in 5th it just coast and your not passing anybody. But can you do any tunes or engine/transmission upgrades with it being 5 speed to get more top end power?

 

It's capable, at least... But, I don't know anyone the makes tuners for it. Wouldn't hurt to call around.

How many miles on the truck? Last time it had a tuneup?

 

Reach out to Ryan Hogan and team at www.frptuning.com ; He should be able to help you. I think the 03 will support HPTuners.