Don't know if you have figured out your problem. From the comments I could also not tell if this is an electrical issue or an engine issue. Twice in the past year we have been traveling on the road around 60 MPH and suddenly the power went away. When slowed to 20 MPH we could just barely move. Took it to the CAT repair. Problem was two sensors. One reads barometric pressure and the other altitude density.
We had this problem diagnosed and the first repair shop told me of the problem and replaced ONLY one of the sensors. The problem happened again 9 months later. This time a full CAT dealer said, they diagnosed the problem correctly but the manufacture say even if only one sensors fails or is acting up, BOTH sensors must be replace. The repair bill was $1400 however the dealer, HOLT CAT in Sacramento CA was able to get CAT to warranty the work of the other dealer and it cost us $310. Yes, $310...you read it correctly.