04 2.4 doesn't shift until you let off the gas pedal

[HVYCVR]

Hello all. I'm stumped and need some options.
We have an 04 2.4 Sonata. It used to run fine.
My daughter drove it to the gas station (just a few miles)
added fuel and upon trying to re enter the flow of traffic on the hwy it wouldn't drive over 45 mph.

I looked at it and the primary catalytic converter was glowing orange. I ran the codes and fixed the converter and now no CEL.

Problem is. It revs slow and does not shift on it's own anymore.

I'm not the best import mechanic but this has been a good car and I don't want to crush it. I'm not afraid to do the work, I just need some leads as to where to look. My wife hates it when I throw money and parts at a problem without a solid return on her investment.

Thanks all.

[11SonataScott]

Possibly back pressure due to a blocked / clogged exhaust. Saw a 70's Caddilac Deville with a similar problem years ago. Many parts were replaced before the mechanic figured it out.

[HVYCVR]

when she limped it home I thought the converter was the problem. Now it has a new one and the pipe is open in front of the second cat. Had to cut it cause it wouldn't unbolt at the flanges.
Was driving it to the muffler shop when i noticed it not revving or shifting right.

Thanks