1995 Chevy 6.5 diesel- transmission won't shift

[boarhog]

At 63k transmission refuses to shift to third gear. Could it be a pressure switch?

[DmaxMaverick]

Could be a valve. More likely a seal blown on a band, or the filter fell off inside or has a cracked pick-up tube (top part of the filter). I've seen both happen, and the result was no shift to 3rd. It is also a possible sign of failed clutches (worn out). That problem requires overhaul.

Low fluid level could also be suspect, but I'm sure you already checked that.

[cruzer]

I had the same problem on my 4l80e plus my speedo quit too. It was the rear speed sensor. We would need to know which trans you have.Model of truck?
Sounds like it's in limp mode.