The description is -as already mentioned- perilously incomplete, so I may be making far too many wrong assumptions here, but ONE "cause" for a "problem" may be too much friction from the tape... in other words "sticky tape shed".
MCI's are a little agricultural by comparison, but one "rough & ready" check of things being "happy" on a Studer is to put it into play and -once things are settled- pulling the pinch roller away and observing what the transport does.
On a well-set-up machine, with nice tape, the Studer will continue playing at close to 'correct' speed for several seconds (indicating that the pinch roller is not being "strained" to regulate the speed exactly).
On an MCI, there is no tension sensing like the Studer has both sides of the pinch roller, and they rely on calculating the open-loop tension -rather approximately, if I recall.
The CORRECT way to measure tensions is with a Tentelometer. All other tests are poor approximations which CAN give some indication of large problems, but are really only of use to the trained eye.
If you ARE going to try the "pull the pinch roller" trick, the most important things are thing to observe how FAST the loss of pinch-roller-speed-regulation causes things to start going off-speed. And given the rather agricultural nature of the MCI transport, it's not consistent across the tape distribution. Try it at 50:50 (middle of the reel), then 99:1 (start of the reel) and 1:99 (end of the reel). You'll find different behavior under different load conditions, but under IDEAL (frictionless) conditions, late-model Studers could possibly regulate almost perfectly for several seconds with NO pinch roller.
If you have sticky tape, it's going to grind to a halt quickly no matter WHAT machine you're on, and no matter HOW well the tensions are set... So how good is your tape.
An experienced person who looks at lots of the same model of machine can interpret results when he performs a test on a machine which he has performed on others of the same type... an inexperienced person probably cannot.
Is your machine working correctly? are you "looking" for a problem that you have definitively identified as being present?
If you're "just checking that things are okay" and haven't had any real indication that there's something wrong to begin with, may I politely suggest you STOP right now? I've seen more machines messed up by well-meaning amateurs than I've seen 'improved'.