Low power, again

[btoscano]

Hey all,

I've started experiencing another problem with low power. Last year it was determined that the guide pin in the IP was sticking. I had that fixed and the problem went away... until 2 weeks ago. At first it seemed related to "summer fuel" in "cold weather". I would stop off and add additives, and all better... until next morning so I'd top off and add additives again. But now that doesn't seem to matter. Sunday was just not a very good day for power and it just sounds worse at idle. Is it a new ULSD?

So far I've changed the fuel filter, checked the air filter, pulled the intake hose and verified the turbo still looks good, pulled the fan belt to make sure nothing is very tight, jacked up the rear wheels to make sure the brakes feel okay, and pulled the bed and checked the tank (clean, clean, clean). Some of those things were just too easy not to check so I did them just as sanity checks.

The real surprise is that I've noticed what I think is higher than normal boost levels by 3-4 psi. I don't recall the truck running 5 psi uphill in 3rd at 30 MPH. I also don't recall it requiring 5-6 psi to run downhill on the freeway at 72-75 (used to 3-4) and 10-12 uphill (used to 8-9). However, maximum boost also seems lower... So it almost seems like the timing has been retarded except that smoke has NOT increased and max boost has NOT increased (and maybe decresed 1-2 psi). Is this ULSD??? Winter fuel???

Any ideas?

Thanks,
Brian