Irregular Shifting

[J.J's6.5]

The past 6 months, my truck will not shift into overdrive at all. It will downshift when it shouldn't, and will slam into gear. If I let off the throttle sometimes it will shift up a gear. In addition my speedometer will only work till about 40mph.

I tried a code reader and nothing showed up

I'm new to this site, any help would be greatly appreciated.

[JohnC]

Check the power to the trans circuit. the ignition switch has separate contacts that handle the trans and speedo and if they are flaky they cause these kinds of problems.