Kip,
Without a lot of electrical accessories, i.e. stereo, air conditioning, power windows etc., there is little need for a high amperage alternator.
The 35 amp would seem to be plenty for a stock truck.
Dropping resistors don't apply to ammeters. Since it's part of the charging circuit, any added resistance would 'confuse' the voltage regulator and probably release the smoke hidden inside all electrical equipment.
