4L60e transmission. No reverse, slipping park 1994 GMC Jimmy

Used to go in reverse, but took a hell of a lot of throttle to actually back up. Now no longer reverses at all. Having trouble getting park to stick as well recently. Looking for any ideas before I get under the car and take out the transmission.

The only idea I have is to check your financial situation.
The transmission may have only needed minor work when the reverse slippage was first noticed. But now suspect it is toast.