Manual transmission slipping

No. But a rebuild will.

nice double post, do we get 3?

if your transmission has been slipping, it means that the clutch plates and steel plates have gone. youre going to have to have it rebuilt or swapped out for a rebuilt one.

A transmission filter should never get dirty enough to prohibit the valve body and pump from getting enough fluid. unless you have driven the truck through deep water or heavy off road use.

The 99 suburban has a 4L60E or 4L80E transmission. depending on the chassis package, If you have a 1.5" rear yoke diameter(the thing connecting the trans to the driveshaft), its a 4L60E, if its larger you have the other. The trans are usually good for at least 150K miles under normal use.

There is a point that a machine works and a point that it stops, you need a transmission rebuild.

Does ur beamer have automatic or manual transmission?

you have worn clutch plates inside the direct drum for the foward gears. they last on average 100,000 miles give and take 20,000 miles

Low transmission fluid is usually the only reason power engages late or slippage occurs. But changing the transmission fluid again would not hurt. The stuff really shouldn't deteriorate like engine oil. Be sure to not run the vehicle many miles until the problem is completely resolved < 100 miles. One easy check would be to make sure the transmission lines are well connected and maintain pressure as well as fluid level. The good thing is that Toyota has a reputation of very good transmissions.

You can have the clutch and the pressure plate checked. If it is an automatic tranny you may try to drain the fluid and have it replaced or have the solenoid cleaned out or checked. The solenoid controls the hydraulic pressure to the clutch

The problem is most likely internal. Sounds like it could be the synchronizer or maybe the gear itself. Hard to say until you take it apart and look at it. I guess a price range of around $1000-$1500 to rebuild, repair costs depend on what parts needed, cost of parts, labor/time involved.

Pull the trans dip stick and smell it. Does it smell burnt? Your tranny might have gone out. I had an Avenger that the tranny went out at about 60,000.