TippleUnduly wrote:
One mfr. told me it was because they could not count on GM to deliver when needed.
This is absolutely true. In the last 6 years GM has idled Express cutaway production twice, and the 2nd time the 4500 version was put on hold indefinitely. It took 2 years for that product to resume, and probably only did so because Ford stopped offering the diesel, so GM saw a market share opportunity.
Also, the Express 4500 still has less capacity (front axle and GCWR) than the E450, so if a maker wants to use one chassis for their entire line-up, only the E450 can fit that role.