Q: Engine bogs down in First

If the exhaust was blocked by the cats before, then some of the debris from the cats [catalytic converters] could have gotten into the pipe to the muffler, or blocked the muffler. Check to see if you can rev your engine without trying to drive it. If the engine still lacks power and the exhaust pressure is excessive, then the cats would need to be disconnected to see if the engine runs better. If it does, then the blockage would have to located in the complete exhaust system. The fuel pressure, if low, would not allow the engine to run above idle either. I recommend having a mechanic, such as one from YourMechanic, investigate your loss of power issue by inspecting your fuel and exhaust systems.