Power loss under load - fan clutch? Alternator?

[Kiasis]

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.

[leolkfrm]

NAPA will have the alternator you need
what kind of temps are you seeing?
when you say it revs, what kind of rpm?

[gmctrucks]

With that many miles I would replace with free flowing Cat I know Ebay has them cheap just this can save you ton's of problems. Now I do think that the fan clutch can cause that problem check around it and see if you see oil leaking from the bearing area also it will be loud all the time when it's bad someone confirm this with me. Now also did this problem happen after they replaced the engine or is this all of a sudden? I'm asking because maybe they hooked something on wrong or it can also be the engine timing see if the timing mark moves when you place a timing light on it maybe the problem is in the distributor.
Good luck! GMC

[stumpuller454]

Dang i wish i was at home to go through my manuals.... hope to be home friday maybe i can help then unless somebody pins the prob...

[stumpuller454]

Just wondering if this problem happend when the new engine was installed or over time has happened to the new powerplant, has a compression test been performed?

For the symptoms you explained i would check your throttle plate operation it could be binding in the bore also check for collasped fins in the MAF, and check all intake piping for any colapse or restriction. A stuck EGR SHOULD throw a code but can be visually checked. maybe a plug should be pulled out and inspected plus gap checked.

let me know what you think, got to help a fellow Big Blocker out!

[PAPA BEAR]

Just a couple of guesses try a new fuel filter or it may be a torque converter problem

[stumpuller454]

Any update on your problem?

[Kiasis]

Thanks for all the input, gang. No update, yet. My local mechanic who installed the rebuilt wants it back w/ the horse trailer hooked-up so he can see what I mean by power loss under load. I'll print out all the advice/thoughts above and take that with me. If he continues to be stumped, I'll come back for more ideas. He doesn't think a going-bad alternator or worn fan clutch could be the problem, but.... something is definitely wrong. Since the problem is a lack of torque, I'm intrigued by the idea of a torque converter being involved. Think I'll research that some more. Thanks again all.

[leolkfrm]

heat build up can give you problems. You didn't say, is the rpm going all the way up but no power to the wheels?

[Kiasis]

Whether the engine is hot, warm, or cold doesn't seem to matter. Tach goes up, but power is very slow getting to wheels. Until this problem, when the pedal got pressed, you could feel the power matching the tach's climb. No more.