Motor flush will do the trick for the 93 Suburban, but make sure you carefully read and follow the directions on the package.
Personally, I would not take the chance that motor flush, mineral spirits, or kerosene might eat away at the seals without first trying Mobil’s Drive Clean oil (on both cars), doing a couple oil changes in quick succession to try to get the sludge out. If that doesn’t work, then you might try some motor flush. I think Mobil Drive Clean oil comes in synthetic and non-synthetic varieties. I would use the non-synthetic variety. After the problem is solved, you should switch to a non-synthetic high mileage oil of any brand on the suburban.