Hi,the problem is the gearbox not the engine definately,as the gearbox cannot control the engine revs.
Does the car pull away ok in drive? Does it pull away any differant in low? as it sounds like it may be either stuck in high ratio.
Or if it is pulling away ok and then changing ratio it,s getting stuck in high ratio,which is why you are only pulling 3700 revs.
Have you checked the throttle cable?This cable comes out of the gearbox next to the dipstick tube and connects to the throttle body,make sure this is connected as if the car has been kicked down hard the cable can jump out.
If you need any more help e-mail me at rbtrans@hotmail.com
Richard
Ive been rebuilding gearbox,s for over 14 years now,and have built well in excess of 150 of this type of gearbox.
Richard, October 2008