Engine stalls at an Idle in drive when stopped?

I had to have my transmission replaced recently when driving through Chicago as my transmission fluid pump exploded and threw pieces shredding the rest. Bummer! I paid a lot of money to have it fixed/replaced. Since getting it done, my car stalls when I pull up to stop signs or red lights. If I can avoid stopping completely or if I put it in park, it won't stall. It gets worse throughout the day or if it is hotter, it seems and will jerk a lot when trying to slowly come into a stop sign or light (or my garage). It also has a hard time getting up hills. The shop that fixed my car says it has nothing to do with their work so won't look at it (plus they are three hours away anyway). They said open and close the hood and jiggle some hoses as it is an airflow issue. That hasn't helped. I don't know if I should demand the original shop fix their work or if it is literally unrelated and I should just suck it up and pay more after I just laid down $6,000 to fix my car. If it is something I can fix myself, that would be great!