1987 Jimmy Engine Probs

[bugmenot]

Hi there, I'm having probs with my Jimmy. It's got about 200k miles on it, but the engine is a new crate engine that was put in about 50k miles ago, as is the transmission. So I took it to a mechanic to get a new clutch put in, but now I am having severe engine problems. When I start the car it will immediately cut off. If I press the gas while starting it, the rpms dont really go up. They will a little bit but it will be erratic; in fact a lot of times when I press the gas the rpms will drop and the engine will cut off. I had brought it back the mechanic to fix but they did nothing. They said the trailer hitch I had recently gotten installed was connected to a fuel pump wire, but this is incorrect as I checked the wires. I should note that prior to me getting the Jimmy the fuel pump was hardwired to a switch so it could be manually turned on and off, but the mechanics grounded this switch making it inoperable. I suppose I'm wondering what could be the problem here? It definately loses power and is not getting enough fuel, so could it be the fuel pump?

[bugmenot]

Oh and the switch was installed because there was some short the previous owner could not identify