Gears won't shift over 1000rpm

sounds like tranny problem to me. I'm not sure what the issue would be with the tranny so take my words lightly. is it the original trans?

 

Have you tried double clutching the beast... and
replacing the fluid..

..... Philip

 

Most likely it is a Eaton Fuller, those transmissions were sensitive to fluid, double check what Eaton recommends (I think it was SAE50). Many people have used 75-90 and those transmission shift very hard with thicker oil. I'd drain it out, run some thinner engine oil through it, just run around a yard bit in the lower gears to flush it. Then drain it and fill it with the factory recommended lube.

There are 2 plugs on the side of the trans. The top one is the fluid level, the bottom one is the drain.

 

Make shure you remove the top plug first... Dont want to drain then find the fill is siezed..

I use ATF to clean and flush...

... Philip

 

i did that once. drained it and couldn't get the fill plug out ended up having to measure the fluid and take the shift tower off and pour it in threw the top.

 

I think I've got the same Fuller six speed in my "99" FL-60 Service truck, rude grumpy little transmission that I've learned to master over the last six years, I change the fluid every year regardless of mileage and never use the clutch except for starting and stopping, Freightliner recommended 75W90 synthetic. Works fine for me but the truck is always in the shop summer/winter so never sits outside over night. Yes plugs are on the passenger side of the tranny ( if it's the same as mine) just shy of 16000 hrs on the truck, lots for a little guy.