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2003 Siverado fighting itself at speed and under acceleration


May 28, 2020
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2003 2500HD, 6-liter gas engine, 160,000-ish miles, daily driver on street. The truck seems to be fighting itself at speeds above 60 MPH. I can "feel" the truck fighting like it's geared too low but this is a recent phenomenon and the RPM's show otherwise. The drivetrain noise increases while above 60 mph and when I let off the gas the truck immediately begins to slow down and the noise goes away. RPM's while between 60 and 70 mph is between 2,000 and 2,500.

Any suggestions as to where to start the diagnostics?
Bueller? Any thoughts on where to start diagnosing? I have no check engine light on so would it be worthwhile to scan for codes anyway?
I have no experience with newer trucks or really with auto's but it sounds like a transmission/torque convertor issue to me.
Is it a 4wd?
is the t case failing? Search pump rub

does it coast well?

how's the front unit bearings? They can be surprisingly shot without knowing it

put it in the air and check stuff

time to put your purse down and get your jack stands :flipoff2:
Yes, 4wd. Why would something "sound" wrong only under acceleration? While going down the read at 65 MPH, what stops spinning or slows down once I let off the gas?
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