As it says above, started car in garage; cold engine.

Backstory: Recently, had tran fluid and belt replaced as it was stalling in reverse. Seemed to fix the problem.
Until very recently. Then, this week tranny seems to strain and fluctuate on hills.
Today it sounded as tho' something dropped or popped and now engine produces crazy revving and lowering sounds and emits bad odor.

Belt? Can't see one missing.
Hydraulic system slippage?