RV Repair: chev bigblock gearbox, ford transmissions, clutch packs

Question
Hi Ron,
I took my 91 28' Georgieboy for its first run of summer this morning. It has a new engine by the previous owner but not a gearbox. I noticed that it wasn't happy changing to top gear and that it seemed to be slipping. Low gears were fine. After getting home, I tried reversing it into its place and there is no reverse gear! The linkage is fine and working. No matter what I did, it wouldn't find reverse. Sooo, does this mean a hugely expensive overhaul? Whatever your good advice, I am sure it isn't going to be cheap! Considering a rather low budget, would it be possible to take out the gearbox myself and take it to a shop to save money?
Thanks Ron. I look forward to your reply.

Answer
By gearbox I will assume you are talking about the automatic transmission.
For starters, make sure it's full of fluid as low fluid levels will cause problems similar to what you have been having.  If the fluid level checks out OK, pull the dipstick and smell and look at the fluid on it.  If it's brownish colored and smells burnt, you have worn clutch packs in your transmission and the only way this is cured is by a transmission rebuild.
You can take the transmission out yourself but given how little most transmission shops charge for this end of the repair, I would let them to it.  They have the equipment and transmission jacks to do the job right.  They also have the expertise to make sure the torque converter checks out, the transmission is adjusted properly when everything is back together, etc.
Depending on the transmission you have, most are relatively inexpensive to rebuild.
In my area, I have been quoted less than $ 700 to take out, rebuild and reinstall an automatic transmission.  If you have one of the larger GM or Ford transmissions, they are a little higher.