Need Hand Held Controller Advice....

[Skinny Blinky]

I have an 06 LBZ Duramax with 285 tires, Dealer said that they counld'nt fix speedo & milage they say is of by 30%...can anyone point me forward to fix this matter?
THXS

[DmaxMaverick]

It'll be off by about 8%. Don't know where that dealer got 30%. Cranial rectumitis, I'd guess.

An aftermarket programmer like Predator can correct the speedo.

[50+]

I have 265's on my LLY. It amounts to only 2-3 mph difference at highway speeds. Or in other words If the speedo says 67, Its actually 70mph. This is according to my handheld gps. No biggie to me.