Wow, lucky you! I replied last night but it didn't come through somehow...
Mine does the EXACT same thing when OD is off, it just does it all in third gear instead. With OD, it does it about 40mph where it shits into 4 and then locks the converter regardless of what you're doing (like going up a steep hill) and then it drops to 600rpm looses power, and then I stomp on it and it downshifts and I restart the cycle... If I shut OD off, it does the same thing, just earlier, at 30 instead of 40. I even installed a relay and a wireless switch on the back of the steering wheel, not because 'i can't extend a finger six inches when you take it out of park', but because I have to switch it TWENTY TIMES every time I drive. Get on 202, switch OD off, turn off onto a side street, switch it back on (because it won't lock in 3rd, if OD is on), get back on 202, switch it off, get over 50 switch it back on.
Based on what you're saying, I guess I'm the ONLY one who has the problem when OD is off?