LEM,
Some of the early TriStar models powered by the RB.211-22B engine were a bit underpowered.
Later on, the RB.211-524B4 engine was fitted to the standard body aircraft, with excellent results...lots of power.
The last model produced, the -500 series had a slightly shorter fuselage, longer wing, and much more fuel...12 hours range. In addition, had active ailerons, for a smoother ride in turbulence, amoung other things. So far as I know, direct lift control is not used on any other civil aircraft type. Also used on the space shuttle, for pinpoint accurate landings.
Personally flew the Lockheed TriStar for over twenty years with four different carriers...and she never let me down.