shifting hard

[1stclasslawns]

I have a 97 K3500 4x4 crew cab with 5.7 vortec and automatic tranny,

I have noticed in the last few days it is shifting vary hard into high gear, I am not sure if it is at torque converter lockup, or 3rd gear to 4th. Depending on acceleration it is between 38 and 50 mph.

Any ideas?

Thanks Jim

[BW4486]

check trans fluid first / it could be as simple as that