'95 KW W900 with a cat 3406e Speedo/tach/cruise problems

Your cruise will work with the transmission removed. That tells me that the cruise works off of engine RPM and speed is irrelevant.

 

The high idle feature will but road speed cancels it

 

Usually cruise minimum is set to 35 or 45 mph ..in that range it doesn't work

 

If that were true it wouldn't let off the accelerator on long grades

 

No it will still believe your going the same speed

 

Just from rereading the thread I think you have corrosion somewhere in the circut. Or a wire just barely hanging on being that it effects multiple gauges the common points are the truck side of the ecm, power and ground to the cluster, the firewall plug and the cluster itself which is unlikely. If the engine speed sensor was having problems it wouldn't effect the Speedo and the truck would likely stall or miss

 

My Freightliner Cruise was out for a year + b4 I found out about 2 Nd sensor on top .Changed and that fixed the cruise

 

If there’s too much gap speedo will be erratic. Don’t know about causing other problems though .It needs to be turned in and backed out just a bit. Otherwise speedo does nothing then kicks in at 10 mph or so and goes up high and acts crazy.Your speedo should have switches on back to adjust for different tire and axle trans ratios