Chevy truck

I have a 1999 Chevy Z71 half ton pickup with about 180,000 miles on it. The transmission starts shifting really hard after about 5 or 6 start and stops. I can park it for about 5 mins and then the cycle starts over. Any ideas or suggestions?

Service it,with the correct fluid and filter-Kevin(messy job,but not hard)

Pull the transmission dipstick and check the fluid level. What does the fluid look like? What does it smell like?

Has the transmission fluid been changed in accordance with the manufacturer’s maintenance schedule?

I’m only asking because you didn’t provide this basic information.