I was told it sounded like the engine was misfiring. I change the rotor and distribution cap. What else should i look into since it is still making that noise/shaking. It happens when i go around 45mph, or slowly press on the gas.

Can you do this?
Place your hand at the end of the tailpipe when the engine is idling. You should feel a steady stream of pressure coming out the pipe. If you feel a puffing or popping from the pipe it would indicate a misfire is occurring. Things like a cracked spark plug, plug wire not all the way on, or a possible vacuum leak resulting in a partial lean misfire.
Don't want to have you replacing everything, but a questionable coil could cause the problem I think you are describing.

Hanky,

I will try this when i get home. Would an exhaust leak cause this? As I mentioned the engine idles pretty smoothly when on, but once i get to about 45MPH it starts to really be felt. Do you know where i could find a diagram on how to set the timing on the car? I was messing with it, and want to make sure I place it back to how it should be when stock. Where could i find this information and what the marks mean on the little pulley thing.

There are some marks on the crankshaft pulley. Among them should be a line that has either a 0 or TDC mark on it. You will need a timing light to do this for best performance. Can you get hold of one someplace? Some stores will rent them out.
There should be an engine emission decal under the hood . It will spell out what you need to do to set the timing. If one isn't there I would suggest that you invest in a Haynes Manual. It is a little involved to explain and a few pictures would help an awful lot. There is a base timing set procedure that is used with a Spout (spark output) wire disconnected. The specifications you need to use would be on the decal or in the manual.

Hanky,

My friend has a timing light so that wont be a problem. I did check the exhaust and it feels to be pretty constant however there is a split second there where i feel a change in pressure. Not sure if it would be a constant flow, or if that signifies that there is something wrong.

1993 Ford E-150, 5.8L conversion van "check Engine"
 

I have a 1993 Ford E-150, 5.8L conversion van with basically the same problem. Have replaced EGR, EVRP, PCV and hoses. Soaked the engine compartment in soapy water trying to find vacuum Leaks. NO LUCK. Checked voltages of sensors and thus far found I am not getting battery voltage to the EGR solenoid (9v at solenoid). Have backtracked voltage to connector #121. Will be checking voltage output from engine compartment fuses to powertrain control module, and onto connector #121.
aside:" check engine" light does not come on until ther vehicle is in gear and moving. Can start the engine when it has been sitting for days and run engine for hours while parked, and Check enging light does not come on. Possible VSS