1998 Chevy Monte Carlo Z34 Transmission (auto) problem

transmissions

#1

I’ve got a 1998 Chevy Monte Carlo Z34 automatic.
The other day the transmission decided to get mad at me. Here’s the situation -
When I was at a stop then accelerated, the car would shake a little and take a second to shift and move forward. Then the next day I reversed out of my driveway then put it in drive and it was as if it was still in neutral. The RPMs would go up but it wouldn’t drive. I had to take it down to 1st gear to move forward. Reverse continued to work. I found that I could manually shift the gears up by speeding up then shifting to 2nd then speeding up to go to drive, but then when I hit the brake, I had to start back at 1st or sometimes it worked from 2nd. The car is not a manual shift so that didn’t seem safe to keep doing. It has plenty of fluid and I can’t find a leak.
Any ideas on what it can be and what I should do?
I didn’t plan on keeping the car much longer as I’ve wanted to get something new. I’ve had it for over 10 years and kept up with maintenance on it. Its otherwise in decent shape. Now I have no idea how much this would cost to fix and if it’s worth it.
Please help.
Thanks!