In the past 3 weeks I have replaced my exhaust manifold gaskets, head gasket, timing cover gasket, sparkplugs, valve seals, thermostat, sls air accumulators, air and oil filters. I've also redone the interior electrical and fixed all the issues inside. Had the car exactly how I wanted it..... Then....

(also, shifter bushings have been rattling for the past year and I've got 220k miles.)

Today, as I was backing out of my parking spot, I shifted from R to D. I heard a heavy mechanical noise which I assume was the transmission blowing. The engine disengaged, and the accelerator had no affect on the car.

Now, I can put the car in park and it keeps rolling.
I put the car in drive and hear a metallic clicking type of noise when I accelerate.
I put the car in reverse and there is no affect.

What can I check to diagnose? Could it be the linkage and how can I check?? Thanks!