San Jose is saying it is running bad at lower elevations, if it is rich enough to loose power to have to go into 1st at a low elevation it would cease to run at 10000 feet. I say start by checking your mechanical advance in your distributor

Last edited by sstock; 10/10/2018 2:01 PM.

1953 Chevrolet 3100
261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done
In the DITY Gallery
Video of the 261 running

1964 GMC 1000
305 Big Block V6, sm420, the next cab off restoration