Long shot, but is your engine shut off lever on the IP all the way up when starting?

Engine shut off is vacuum controlled from a vacuum valve within the ignition switch. If there is any vacuum leaks in any of the vac hoses it may introduce a partly closed shut off at the IP (fuel on/off) due to a vac leak it may start harder, but once running generates more vacuum thus opening the shut off all the way. Just a thought!

If you did an Ohms test, you would know for sure if your GP's are good. Now check and see if they are getting 12-V juice.