Dodge Repair: 1991 dodge d350 5.9 cummins, wheel drive cars, front wheel drive cars

Question
QUESTION: I have the earlier 1991 version of a dodge truck with 125,000 miles on it. About 2000 miles ago I started to experience hesitation in power at highway cruising speeds and am unable to maintain speed up hills the same as I had before. At first I suspected a clogged fuel filter from possible bad fuel from a gas station so I changed the filter twice over a 1000 mile period and saved the fuel from the filters for inspection (which looked clean and clear).  I also replaced the air filter and inspected the turbo for any damage. I also inspected the rubber connections for any cracks, and found nothing unusual. While driving down the road my rpm runs at 2000 at 58 mph, egt of 650, and boost at around 7 psi. When I start climbing a small incline the boost goes up to about 13 psi (it would usually go to about 15-16), egt goes to 800 and speed drops to 1750-1800rpm at 48-50 mph. Do you have any other suggestions for repair?

ANSWER: Hi Keith,
I would believe that there is self-diagnostic capability in the engine controller. Turn the key:"on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then watch the check engine light (which remains "on") to see it begin to flash, pause, flash, etc. Count the number of flashes before each pause. Then repeat the process to assure an accurate set of flash counts. Then tell me the counts in order of appearnce and we'll go from there.
Roland

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QUESTION: I don't have a check engine light on this vehicle.

ANSWER: Are you certain that it might not be burned out?

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QUESTION: I am totally certain this truck doesn't have a check engine light.

Answer
Hi Keith,
Without such capability I can only suggest checking the compression and the use of a shop-level engine ignition analyzer/scope. I admit that I am not as familiar with that engine or in fact with the truck line as I am with the front wheel drive cars. I have not obtained the shop manuals for truck except from '04-07. Best of luck however.
Roland