Q: Loss of power won't go over 35 mph - 1999 Dodge Ram 1500

This may be a sign of low fuel pressure, a failing mass air flow sensor or potentially a clogged catalytic converter. As you may already know, the catalytic converter converts toxic exhaust gases into less harmful pollutants that are suitable to be expelled into the atmosphere. When this is clogged, this causes these gases to be backed up into the exhaust system not allowing the engine to breathe properly (think of a backed up sink). When this happens, the engine I forced to work much harder to expel these gases. This often results in the engine bogging down and causing very poor fuel economy. This should also cause a Check Engine Light to come on as the O2 sensors should be reading the incorrect amounts of oxygen in the exhaust gases if this is your problem.

The mass air flow sensor is a unit in the intake system that monitors air intake as it is mixed with fuel prior to being injected into the motor. When this fails, this can cause an imbalanced air/fuel load to be supplied to the motor which often times results in the engine starving for air or fuel. This is what causes the hesitation or loss of power you describe. This can also cause the engine to struggle to idle for the same reason. I would suggest having a professional from YourMechanic come to your home to diagnose and replace this sensor.