Is my transmission going bad

[02chevy1500]

I have a 2002 chevy silverado 1500 with 78k miles.

The trans sometimes has a hard shift going into second and when you put it into reverse it makes a clunking noise. I also had 2 incidents where it would slip and there would be nothing when I'm driving and then I'd restart the truck and it would be fine. In between those 2 times, I have put 1000 miles so it is very intermittent. What is going on? I was told it was the trans going bad by a shop but nobody wants to believe it with that amount of miles. Can anyone help verify what the problem could be?

[Graham184]

I had a hard 1-2 shift as well at 110,000. Just did a fluid and filter change, and disconnected battery for 5 min to do a sort of reset, i think. It shifts wonderfully now while underway.

[02chevy1500]

A guy told me that the plug on top of trans pan on passenger side can get fluid in it and it can cause the problem. I've never heard of it happening but I'm going to check that. And fluid is about 4 months old

[Texas Red]

I have pulled away from a stop light a few times in both 05 Sierras and had what can only be described as a slip. It's as if the converter decides not to go, then I let off the gas and try again and away I go. My last 05 Sierra started this at about 114k and did it all the way til 385k albeit sporadically and not very often. The 'new' 05 Sierra has 90k on it and it did it twice the other day. Not sure about the hard 1-2 shifts.