About German tanks: AFAIK the Germans had stopped development of new designs after France, because they where convinced they had the best tanks in the world. This didn't change until they met the T-34 and KV-1 in the field.
If you want to change history in any meaningful way, you can't just have the Germans waiting 6-12 months, you need to give them better intel about Russian tanks.
And remember, the Russians had only just started production of the T-34 and KV-1. One of the reasons the drive on Moscow failed was that the Russians finally managed to get large numbers of them to the front. For every month Germany waits, the Russians get mote steel monsters.