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Message: <blockquote data-quote="INW-Iron-Steel" data-source="post: 21935" data-attributes="member: 11733">Because of this, I would assume your stepper motor is on the way out. This is a very common issue with GMT800 clusters. When one stepper goes, it is common for the others to follow. I replaced my cluster at 230-ish because of a failed oil pressure stepper motor. Mine would move to the right when I started then engine and then get stuck. When I re-started the engine the next time it would move again and then get stuck at a higher pressure until the needle was stuck maxed out all the way to the right.IMO, The fuel pressure gauge is a good idea, but a decent scan tool will be able to tell you your oil pressure as seen by the ECM. This would be a good way to verify gauge/cluster issues VS oil pressure sender issues (these can also be somewhat troublesome on LS based engines). When you have the diff cover off, jack the truck up and put it on jack-stands. Pull the rear brakes (this eliminates drag on the axles) and drop the rear of the driveshaft. Spin the yoke by hand and feel how the bearing is moving. Try to move the pinion up and down at the yoke. Also try to move it in and out. You are looking for play here and don't want any. This is different from backlash, which you will feel/hear as a bang-bang as you turn the yoke back and forth before the gears engage. If you have some grease, it works OK as gear compound and you could run a pattern on the gears.FWIW, the 99 4.8 in my Sierra holds 30PSI oil pressure at hot idle. I see just over 40PSI cruising at temp on the freeway in overdrive. That is with my preferred 10w30 HDEO. Somewhat recently I was seeing 20PSI at hot idle, but that was a one-off type of situation.</blockquote>