trans vibration in 3rd

[mikeku91]

right when i hit 45 and i think thats 3rd gear getting up to speed on the high way my truck vibrates and jumps forward, after 60- 65 mph it goes way.....if i put the truck in tow/haul mode (turning off the over drive) trucks fine, no vibration or jump i have a feeling its the trans truck does have 183000 miles and i think it has the oem trans in it still.....does anyone have any idea what exactly it is or how i can test to see if it is in fact the trans
Thanks
mike