New Mamba 25 Esc Problem

I have a new mamba 25 esc in my mlst and I can't get it to work ...every time I try to set it to the transmitter/receiver it seems to take it then when I run it it crawls even at full throttle then the esc gets real hot ....if i put the old mamba 25 it works fine...reason I changed to new mamba 25 is the old one is too old to program with pc...anyone un into this