Can't remember the factories in Stalingrad off hand. The Tractor Works was one I believe and something October....., boy do I feel stupid without my resources with me. In Leningrad they did produce tanks and many went out without paint.
I believe that late in the war , especially after the Tigers and Panthers hit the front, the Soviets started to upgun their T-34's because the 76mm was pretty useless against them. I think the T-34/85 came out late 43 or early 44. Again without my references handy i feel blind.
I don't believe the commander had any internal communications with his crew, this was indeed a problem for them.