vp44 intermittent power loss

'99 dodge ram with 120,000 miles on it. The lift pump and vp44 replaced under warranty at 65,000, has been trouble free until recently. Seems to be the same scenario others are experiencing with a little twist. It
will run fine until it "de-rates'" and loses power, but can usually maintain 55-60 mph. If you let off the throttle momentarily and apply again, it will usually pick back up. There is no set pattern, it happens randomly. There are two codes present, unfortunately I don't have them available with me, but the ecm failed code comes on immediately after they're cleared, the fuel pump code ( part of it is p-16 but can't remember) doesn't show until it actually loses power. However, there are no problems (yet) when the ambient temp is under 80-85 degrees, which leads me to wonder several things:
ecm breaking down electronically due to heat vp-44 - same scenario fuel temp too high causing low viscosity / poor lubrication
I should add that I replaced the lift pump, but have no way of checking pressures. It worked fine for an hour driving to the beach but then starting it again. At times there is little to no throttle response at cold startup when ambient temp over 95, as in at the shore. I am capable of replacing the pump or ECM myself, but don't want to throw parts at it without more diagnosis.

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