2004 Coupe - 35,000 miles

My car has developed a shudder vibration, when it downshifts into the lower gears. If I push on the gas when this symptom occurs, it acts as if it is limp mode, but it always kicks out of it once I let off the gas and the car slows a bit. There is no whining sound and it shifts fine at highway speeds. I wanted to check the fluid level this weekend, but couldn't find the dipstick for the tranny, I also read in another post that the TCM could be an issue.

Anyone have any other thoughts as to what I may check, I wouldn't think the fluid would need changed with on 35K on the car.