E4OD problem: TCIL light flashing, codes P0755 and P1728

Recently, the E4OD transmission in my 23' Maverick Class C Motorhome began acting up. Basically, it seems to work fine when first driven cold, and still works correctly on the highway, but the shift to 2nd gear (either direction) is very harsh. I'm hoping someone can give me a clue about what might be wrong, or point me to another group or web site that might help.

The facts:

• '97 E350 chassis with 85,000 miles - no prior problems

• "Service Engine" light comes on with no apparent change in transmission behavior. This first began about 4000 miles before the next indication, and the tranny was still shifting properly.

• TCIL (transmission control indicator light) starts flashing while driving. The TCIL is reset every time the engine is stopped. When driving again it eventually comes back on at the moment the engine loads enough to begin the shift from OD to 3rd (like starting up a hill). It seems to coincide with the initial unlocking of the torque converter, I think.

• When cold, transmission appears to operate smoothly and correctly, generating no codes.

• When hot, and after "Service Engine" and TCIL lights come on, highway operation appears normal, with the usual shifting between OD and 3rd going up and down hills.

• When hot, and after "Service Engine" and TCIL lights come on, it will hang in 1st to at least 30 mph, unless I back off the accelerator, which gives me hard shift to 2nd. If it downshifts from

3rd to 2nd while under load (hill, say), the engine will race momentarily, then it's a really hard shift into 2nd.

• Switching off OD before the TCIL light comes on will prevent the P1728 trouble code from showing up, but letting OD be used again will soon have the TCIL flashing.

• The trouble codes: PO755 (shift solenoid B); P1728 ("slip" code)

• The transmission shop said the fluid looked new, with no sign of slipping symptoms (odor and color changes). Current fluid is about

25,000 miles old, and I've had it changed every 30,000 miles.

• The same transmission shop didn't want to attempt any repair without more obvious signs of trouble, since it seemed fine when cold; i.e., it might be a wiring problem, possibly the control module. They said the hard shifts were likely normal for a transmission with a trouble code, as it tries to "protect" itself from further damage.

So, any ideas? I've been to a Ford dealer, and independent auto repair shop, and the transmission shop, with little to show for it except I'm out $150 in diagnostic costs.