my 2000 dodge van with a 5.9 and 3.92s is close to that fluctuation and it definately locks solid in lock up. It will not hold the speed as precise as my 2011 1500 ram did on the data stream on my scanner or in real life on the freeway running side by side.
I have a set of 3.21s to install, I am positive they will give me better highway MPG.
Interesting, my scanner would stay at 60 then going down a hill would creep to 61 but rpm would go down to 1888. All over the place. I'm thinking the converter is not locking up to well (all new parts, electrical and trans). Will the lockup fluctuate 100 rpm?
I have a set of 3.54 for the Dana that I would like to try. Talked to the Dodge service man, he said no problem reflashing pcm for the ratio change.
