Auto Stag RPMs at 55 mph

[Mike Wattam <101714.1343@domain.elided>]

The theoretical gearing of any auto Stag should be 19.8mph per 1,000 rpm.

However, whatever speed you are doing, there will be an element of torque
converter slip and this is minimised at high speed, say over 70mph.

In the conditions you describe, as long as you are certain you are actually
in 3rd gear, there would be one of two problems;
1.      something wrong in the box, like maladjusted bands
2.      something holding the car back, like seized rear brakes

Stag driving should be very pleasant indeed.  Have your friend sort it out
and try again.  Then buy one.

Mike Wattam
Triumph Stag Register