Okay, this is quite odd so maybe someone can help. I changed out my cables recently and was cleaning rear derailleur when I noticed a tooth of one of the pulleys broken off. So in meantime I ordered a new and had all cables replaced. While on a stand everything spins supper smooth, but when riding, especially going uphill, the chain will jam and not go through the deraiileur and just stay on front chainring. Sooo, could that broken tooth have this affect. As i said it only doesn't run smooth when riding (and mainly riding uphill when there is extra torgue). That tooth could have been broken for a long time and I had never had problems. I also did put on a new chain (it almost feels like a stiff link getting jammed but that is not the problem.)

I am no professional but have worked on my bikes for years and this really perplexes me. I just can't believe a broken pulley tooth would cause this.