Hi all, We haul horses. Truck started losing power under load. Fine without load. Example - now feels w/ one horse how it used to feel with four horses. Engine revs, but power just isn't getting to wheels. 1999 K2500 (old body style), 454 engine. 100,000 miles on truck. 5,000 miles on rebuilt engine (blew up on a stuck thermostat hauling horses over the Sierra Nevadas at 3:00 a.m. - bummer). Three shops say no tranny problem. No slipping, no hestitation, no contaminants. Three shops say no CAT problem. Tested back pressure and all's fine. Three shops say no fuel delivery/fuel pressure problem (56.5 psi). Today, shop said fan clutch and alternator bad and that could account for some loss of power. Okay, if they're bad, they're bad and I'll replace them. Can't find AC Delco 124 amp alternator from anyone except dealer at $315. Can get 120 amp or 140 amp for $125 and $150, respectively. Question(s): Can I use the 140 amp, or am I likely to screw-up something else? If not, is 120 amp close enough to 124 amp that I'm not under-powering system? Rock Auto lists the 120 amp w/ the same part number as the 124 amp from the dealership. Anyone think it's the same critter and Rock Auto is 'rounding' to 120 for simplicity sake, or is it not the same alternator? More importantly, anyone got another guess at why we're losing power under load? Just doesn't have the torque to pull like it did. Starting to move the entire ranch. Need truck to not break down on highway with loaded flatbed or worse, loaded horse trailer. Thanks all.