I have a Cat forklift C-6000 and this is my similar issue. My lift will work find for hours, but seems like when the unit gets hot, or the left out in the hot sun. The lift will go into forward or reverse, but as you give it gas it comes out of either forward or reverse. This happened the other day and and it took me 5 minutes to get the lift back into the garage. The lift would go into forward and move like a couple feet and would pop out of forward. Hope this makes sense. Look forward to your response.
Thanks

...after very time-consuming troubleshooting, I found a loose cable between the encoder (P14) and where it is being connected (green wire) (P1) traction inverter unit

tr_doctor,

I will check them all and will be back what I found

Kind regards,

you have damage in electronics, check diode, igbt and thyristor of drive systeem,