You said about the tread levels, but didn't say what tyres you actually have? That would be the first thing I would be looking at.
2nded. What tyres?
3rded, most important question that hasnt been answered in this thread!!
No point having a spaffy diff, WALK, KW V3's and Fernando Alonso behind the wheel if the car is running on Nankangs lol ...
Wheelspin from a standard Gti in 3rd would suggest that its running on budget tyres imho.