because you're probably in too high of a gear. What rear end gears do you have? Shifting normally (2000 rpm), with 2.73's, I shift to 2nd about 20mph, 3rd about 30, 4th about 40, and 5th about 55 or so.
I don't know exactly why the car is bucking, but I would assume that being at such a low mph in that gear puts it very low on the rpm's, which lacks torque. This is all an assumption though. My car does the same thing, which is why I don't run under 1500 rpm...I'd assume most other people don't either.
What rear end gear do you have? What size are your rear tires? What transmission are you running?
so, according to a spreadsheet I have, after entering your variables, you should be right around 1550-1600 rpm at 30mph in 3rd gear. In 4th gear at 30mph, you should be right around 1200rpm. My point is that your RPM's are too low and that's most likely causing the bucking.
Try to stay above 1500-1600 rpm. 30 mph w/ your setup should be about 2300 in 2nd gear, so just stay in 2nd or speed up a little and hit 3rd at 35mph, which should put you at about 1800 in 3rd (at 35mph) and you shouldn't have those bucking problems.
Run 3rd out until about 46mph (2300 rpm) and hit 4th, which will drop you to about 1800 rpm in 4th at 46 mph.
Run 4th out until about 60mph (2300 rpm) and hit 5th, which will drop you to about 1800 rpm in 5th at 60mph.
I never get out of 4th gear in town with my 2.73's. W/ my GT w/ the 3.73's, I'll hit 5th in the city if I'm around 50mph or so, which is speeding, so of course it's not often My speedo is wrong in the GT though, so I really have no idea how fast I'm going.
I'm not trying to tell you how to drive, I'm suggesting how you might get rid of your bucking problems, because the most likely thing I can think of is too low of rpm. You can shift higher, but I wouldn't shift much lower.
ok guess i was not getting enough rpm`s i will just have to drive in 2nd i drove it like that it seems fine.also after about 35 it doesnt do it in 3rd or 4th thanks for the help i thought something was wrong with the car