I think that an auto would work pretty good with good clutches,bands,low stall converter,aftermarket pan,good oil,and a temp gauge,which I would keep a close eye on if you gotta pull long hills.A built 47RH would be a better towing trans with a lockup converter,but you could buy a nice donor truck for that money,and a 5 speed with a HD clutch will handle it no prob if you treat it decent.Hard to beat the efficency of the manual.