Moaning tranny

97 GC 5.2L I have had this problem for well over a year, but have not had the funds to have it fixed. When shifting from park to either reverse or drive, the transmission sometimes hesitates before engaging. Sometimes it does not engage at all until I rev the motor way up when it will finally clunk into gear. If I drive away with normal throttle under normal load it will shift normally. If I am headed uphill or hauling anything it will slip, shutter and make a moaning noise. When at speed it will slip when I hit the gas and kick down. Does not matter if it is cold or warm out, the problem is the same.
It sounded a lot like a bad clutch in the tranny but like I said, it's been well over a year and I would have thought the problem would have gotten much worse over time if that were the case. I recently replaced the filter and fluid with ATF+3 and while inside, adjusted the bands. Throttle cable has been adjusted as well.
Does this sound like a tear down or is there something else I can look into? Could the torque converter be the culprit? Any suggestions would be greatly appreciated!