Check the ignition timing. Try rolling the wires in the trigger. Go with the way that gives you the most timing.

Your corrected HP is 880. Appears you actual HP on dyno was 817. This could account for the bad MPH. 139 MPH it just aint seeing any HP.

You are not going to set the world on fire with a Powerglide in that car unless you get everything dead on. You need to be in the 7,300 RPM at the finish line. The car should be in the upper 140's to over 150 when everything is good and in good air. I would want more gear probably a 4.88. This will help tremendously. Put some gear in that car and check the dumb stuff and you will be on your way.

Also judging from your dyno numbers. There was 50 HP in the altitude correction. So when you actually run in good air you may need more jet. Bad air less. Best thing is to jet for peak MPH. Don't worry about the other numbers. Go up 2 front and back. If it slows down start going down. Keep going til it runs it's best. Then go up 1 for a little insurance.

Leon