does it have to be a pusher ?
haulmark, renegade, showhauler all make some great conversion trucks with a minimum of 450+ hp & 12speed auto trans.
the conversion trucks don't have a TAG axle - their 2nd axle is an actual DRIVEN axle with duel tires.
the drive axles (both of them have independent locking diff's & the axles can be locked together - if you really need 4 wheel drive ;)
maintenance on conversion trucks lower since access to the engine & trans is easier (no reason to go thru the coach & bedroom to work on the top of the motor).