The engine has some weird rpms, it'll drop 100 or 200 rpms while cruising at 30 every second or so, and only at 30mph, it's fine at higher speeds. Any ideas?

 

Possibly your TPS. Is it throwing any codes?

 

Nah, but it literally just started happening. Hmmm. How do I fix it?

 

Having a tuner to do some data logging and seeing what the engine is actually doing sure would help.

 

On the 545RFE transmission ther is a 2nd and 2nd Prime. The ratios are 1.67 and 1.50. It almost sounds like it could be shifting between the two. The 2nd Prime is only supposed to kick in on a downshift at high speed.
At 30 MPH you can take the rev/mile for your tires multiple by your axle ratio and then multiple by the transmission gear ratio to get what RPM your engine should be running.
Stock 265/70r17 = 657 rev/mile so 328.5 rev in a minute at 30 MPH.
328.5 * 3.55 * 1.67 = 1947 RPM
328.5 * 3.55 * 1.50 = 1749 RPM

What is you RPM when this is happening? It could try to drop into 4th at that speed at 1166 RPM.

 

Should be in 3rd gear at 30MPH when cruising.

 

It's at about 1500 rpms, but it only does it under light throttle, as in very light...

 

the more and more I read about a bad tps, it's exactly the symptoms I am having. Do I need to replace the entire TB or is there a procedure for fixing it?

 

Change your EGR vavle. I did mine two weeks ago, my truck was doing the exact same thing, "bogging" down between 30-40mph and fine at highway speeds. and throwing no codes. Hope this helps