I would suggest your problem is fluid related. My car would 'hesitate' for a second when cold when I got to the first stop sign at the end of my street - then BANG!! it engages. Once warmed up, it was OK.
The solution was a 4 quart drain & fill, followed by a second one a few days later. I did a third after a few weeks to make sure I had fairly clean fluid & the problem has never come back. The proceedure is easy and cheap to try - just the cost of some Dexron III.
You should also consider a tranny cooler to prevent excessive wear in the future.
