Occasionally, when I get on the go-pedal, I hear a strange raspy sound, lasts for about a second, from the tranny when it's getting ready to shift into 4th gear, normally around 50-55 mph.

Tranny fluid is where it should be (though I don't know age b/c I just bought it in Dec so I'll be changing it and the filter soon), shifts nice and firm when putzing around town.

Not sure of the past history on my Ram, it is an '04 with 80k so lots of highway miles, the rear diff is rusty so I figure it towed (and heated the rear fluid so that'll be changed too). No 5th wheel hole, so whatever it pulled, if anything, was pulled via the receiver.

PML pan or Mag Hytec is in the future. Any 48RE Tranny maintenance tips for a Ram newbie? I maintained my Durango's 44RE so I'm familiar with the ATF+4 and auto tranny fluid change schedules.

 

It sounds like it might be the waste gate, rather than the tranny?(Someone whose more an expert might chime in, but that's what it sounds like by your description.)

 

Wastegate - I didn't even think of that, I'm new to the Cummins and the only wastegate 'noise' I've heard comes from the SRT-4 guys who had a big club where I worked in Germany.