Stop using the 76mm on the T29!

Lert: The 90mm has always been available on the T29.   One thing WG could do is:   - Change the M6 tech tree to lead to the T29 after researching the 90mm instead of before like now (IE, make the 90mm mandatory on the M6 rather than optional) - Increase the XP research cost from the E2 to the T29 by 14k XP (that's what the 90mm costs to unlock) - Remove the 76mm option from the T29   This would ensure that nobody ever drives a T29 with the 76mm, and keep the research costs for the full research paths the same.