The Stovebolt Site Forums The Shop Area Driveline Clutch out on 54 1/2 ton

Talk to your local transmission shops. If all they ever worked on was econo box foreign stuff, keep looking. These trucks are not rocket science but I wouldn't trust it to someone that has never seen one before. The second part of your question is more complicated. Your truck has a closed driveline which limits your options on what you can do to get more highway speed. Changing the rear end gears is probably the best and cheapest option. Although it could still cost you about $400 for parts and a similar amount for labor. A 4 speed will not by itself give you better highway speeds as it is still 1:1 in 4th gear. The same with an automatic unless it has an overdrive feature. There are expensive adaptors involved for an AT swap and it will require an open driveline which could require replacing the entire rear end or the differential center section from a later (TF) truck. Finding someone to accomplish this work could be a challenge.
Fred