1.No ideally.but please check if ur no. of re-transmissions is high for higher MCS.Also check what is your initial MCS for transmitting the first TBF.It shouldn’t be higher than MCS-5
2.Same as the reason of TCH Drop along with TBF congestion & frequent LU & Cell reselection.
3.General formula for TESR=Total successful TBF establishments/Total TBF establishment attempts.