Low gear stuttering

2007 Tacoma 4.0 V6 with 135K miles. My problem: Accelerating slowly from a stop, at about 1500 rpms (or 25-35 mph) the truck shudders or skips beats (It can be felt mostly in the gas pedal and the steering wheel). When it reaches 40 mph, the shuddering stops. If I accelerate from a stop at a moderately faster speed, there is no problem. If I put the truck in 4th gear (not D) I can drive around with no problem. There is no consistency as to when it might happen—the problem can go away for six months and reappear, only to disappear again (like when I take it to a mechanic). Gas mileage is around 17-18 mpg. Plugs were changed at 120K.

 

Change your transmission fluid. The original fluid is worn out.