2005 Legacy Wagon transmission delayed engagement?

2005 Legacy Wagon 2.5i, 4EAT, 82,000 miles. For about 18 months now I've noticed a monetary hesitation in gear engagement, or gear slippage, in 2 conditions: (1) within a minute or two of starting, when letting off, then reapplying the throttle (to slow down for a series of speed humps on a slight rise, then accelerate slowly after passing over each); and (2) after 15 minutes of driving, executing the same action going over speed humps on a steeper hill. (This is a route I drive three times a week). The feeling of gear slippage or hesitation may occur in other situations, but rarely; I notice it regularly in these two situations. I took it to a transmission shop a year ago; the mechanic could not replicate the problem, and found no ATF leak. Thinking about it again today, I did some searching and came across the "delayed engagement" threads here and thought it sounded like my problem. But the threads focus on the 1998-2001 4EAT engines. I figure I have nothing to lose by trying the Trans-X leak stop in my ATF, but wanted to see whether there was some other diagnosis of my problem. (apologies: my paragraph breaks get stripped out when the message posts)