700R4 transmission shifting too soon

[Roch2nite]

I have two GM vehicles, 87 C10 and 86 Caprice that both shift into high too soon. They don't seem to downshift unless I press the gas to the floor almost. Then they shift back to high when I let off the gas. The engine starts pinging a little since its being stressed to pull the car in a high gear. I notice this on back roads when I'm doing around 40 - 45 mph. I'm not in overdrive when this happens. The truck has 101K miles and the car has 74K so I don't think its a tranny overhaul, but I once had a 85 Old SW that did the same thing, but it had 155K and I blamed it on a slipping tranny. I check the fluid level and even change the trans filters and fluid, without any change. I'm hopping it only a adjustment or something minor. Any Transmission gurus out there?

Anyone have any ideas on this one????

Thanks,
Larry

[C&C Chevy]

http://www.73-87.com/7387garage/drivetrain/tvcable.htm

[magnethead]

what he said.