I have a problem that my dealer has not been able to fix. The subject car has 124k on it, with the 1st owner having replaced the trans. with a GM unit at about 60k. Just within the last two months, the vehicle 'surges' with a sort of sling shot feel into OD. I can't separate the shift from drive to od from the lockup most times. I do a lot of highway driving, and I notice the problem once getting up to 58-63 and also when resuming speed around that mph after a downshift to pass. It's not a horrible problem, but it never did it before, and it is annoying...any help would be appreciated. Thanks.