sonnydad - the gear on the motor and the transmission need to be matched - the Sentria 2 tranny and a G5 have different gears, so you need to put on the gear from your G5 onto the tranny (the grey color one in your photo on the exterior of the tranny needs swapped. (the gears I am referring to are the ones the belt rides on)
You also might need to adjust the handle slide assembly too.