I can't offer any help on the repair but revving at 4000 at 70 mph in 5th is way way wrong. You should only be around 2500-2700 rpm. It sounds like you have a badly slipping clutch disk. If that's the case, the pressure plate and flywheel are probably damaged, too.
If you can't get it repaired and want to retain a 5 speed, grab an Isuzu transmission, along with it's cables, slave cylinder and transmission mounts. They're much more plentiful than Getrags and it's an easy swap.
[This message has been edited by fierofool (edited 07-13-2014).]