Which brings me to my other question, why is it limited to 105?

 

Its almost certainly gear ratio change confusing the ECU and TCU. 3.77 gears are about 29% shorter than stock, so the sensors are detecting ~29% sooner at the same transmission speed. That turns a ~130 mph limiter into ~100–105 mph.

As for top end being “dead” my 80-100 is about 4.42 seconds (on high 1.31 incline) which doesnt seem too far off from stock.