Overweight, underpowered or defective?

I have a 4 cylinder 2009 Extended Cab Tacoma with less than 2000 miles. When I put my 800 pound Triumph America in the bed the transmission seems to vibrate in 1st gear (automatic) . Is the weight to much or is there a transmission problem?

 

that isnt alot of weight. does the truck sag in the rear really bad when loaded?maybe driveline angle

 

No definite sag. Dropped maybe an inch or two.

 

than i rule out driveshaft angle issue.my 02 4 banger auto never had that problem and i hauled some heavy loads(coworkers)and loaded the bed,and towed a trailer. my 08 is a 6 w auto and no problem. i say go back to the dealer and see what they say.leave bike in the back when you go.

 

It doesnt sound like its underpowered. It has to do something with the driveshaft or line

 

Thanks guys!