Why does your 1993 Nissan truck keep jumping out of od at the same speed?
Off the top of my head, could be a faulty torque converter or the solenoid that controls it. Also if the speedometer is screwy that can mess with it too.
What is the difference between a 1993 Nissan hardbody pickup truck and a 1993 Nissan d21 pickup truck?
Depends what motor. 240SX had the SAME EXACT block with very little differances. Many Hardbody owners switch to the 240sx Intakes and cam. The transmissions however have different ratios. The cams are different too. The "Car" cams had more HP and less torque then the "truck" cams. The "Truck" cams maxed torque a full 1000 rpms sooner too.