Hello, I don't think it is slipping.. I believe its called shuddering ?

It shifts fine until It gets hot, ( driving hard for about 30 mins - 1 hour ) then it starts acting up... then if I let it cool down for lets say 30 mins, Its fine again..

I wouldn't say the gears are grinding either.. What could the problem be and how would I go about fixing it ?

Maybe a solenoid ?

Should I do a trans flush ?

Or should I buy this one off my boss for $300 (130k miles on it)

Thanks guys

- Paul