To me that's a lot, since we don't usually pay anything but what it says on the ebay page.

You say it only happens in the 1-2 shift? Never 2-3 or slow lockup? I'm no expert but it may not be pressure related if only 1 shift is affected. Could it maybe be that the 1-2 piston in the accumulator is slightly binding? Maybe the seal is torn or the bore has a groove or something? If so, when doing the shift kit, you will find out and be able to replace parts if needed at that time.