* Severe Engine Problems: This is the most likely culprit. The popping noise could indicate a misfire (one or more cylinders aren't firing properly), a failing ignition system (spark plugs, wires, coil packs), insufficient fuel delivery (fuel pump, clogged injectors), or serious internal engine damage (worn bearings, piston problems). All of these would dramatically reduce power and cause a popping sound.
* Transmission Issues: A failing transmission (automatic or manual) could also cause sluggish acceleration and a limited top speed. Slipping gears, low transmission fluid, or internal damage are all possibilities. The popping noise might be related to gears grinding or components failing within the transmission.
* Exhaust System Leak: A large leak in the exhaust system before the muffler could result in a popping sound as unburned fuel ignites in the exhaust. While this could affect performance, it's less likely to be the sole cause of such dramatically poor acceleration.
* Drive Shaft or Differential Problems: Issues with the drive shaft (connecting the engine to the rear axle) or differential (allowing the wheels to turn at different speeds during turns) could limit speed and cause unusual noises. However, the popping noise is less characteristic of these problems unless there is significant damage.
* Severe Restriction in the Air Intake System: A severely clogged air filter or other obstruction in the intake system could starve the engine of air, leading to poor performance and potentially popping sounds. However, this is less likely to cause such a drastic drop in performance.
In short: This truck needs professional diagnosis *immediately*. Driving it in its current state risks causing further, potentially expensive damage. A mechanic should inspect the engine, transmission, exhaust system, and drivetrain components to pinpoint the exact cause of the problem. Ignoring the issue could lead to a complete engine or transmission failure.
