95 ram diesel ecm & tire size

I'm having trouble getting into od.I have one step bigger tires than stock.I brought it to the shop and they told me that they cannot correct the problem with the bigger tires(They cannot adjust the ecm)
Can you change speedometer gears??or do I have to put the tires back to stock??
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The tires aren't your problem. My '95 3500 ran 215/75R16's originally (29" tires). I ran 255/85R16's (almost 33") for most of it's life (currently run 235/85R16's - still larger than stock), and never had any issues.
What's (specifically) the problem with the transmission? Have they determined that the ECM is just not activating the OD solenoid? Or is the ECM commanding O/D, but the transmission isn't cooperating? Have they ruled out the TPS? Brake light switch? Have they tried wiring in a switch to force the transmission into OD, and therefore rule out anything in the transmission as the problem?
Or did they take one look at your tires, and decide that "must" be the problem?
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On Nov 30, 6:02 pm, "Tom Lawrence"

factory spects with the bigger tires.I had 245/75R16 and went to 265/75R16.But guess what,doing some research on the internet told me what might be the problem,if it works I will be glad to share.I'm also going to check with this speedo co for a differen't speedo gear.( to match the speed sensor with the gears.Thanks for your input I will check those other items.
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