ok, let’s recap : your UL TBF Establishment Success Rate = 30% in some cells, and the cause of failure is “MS no response”.
Are you sure it is not due to some kind of congestion ? BSC congestion for example ?
30% is was too low to be fixed with parameters fine tuning. You should focus on BTS configuration and hardware congestion or hw fault.
Your UL gprs PC settings were very “safe” 😉
Have you tried rebooting the cell ?
Can you see a pattern ? Maybe all failures are occuring on one specific BSC board ?