Hello, so i purchased a 1990 F250 7.3idi awhile back and I've slowly been working on it but I cannot seem to figure out why it has a hard time starting. I've replaced all the glow plugs and the relay, I know from the previous owner that the injection pump is turned up, probably all the way. I don't know if that would cause it to have a hard time starting or if the pump is just worn. When I plug it in, it starts up every time no issue and runs, never stalls.

 

What brand glow plugs did you install?

 

I'll second that, sounds like the glow plugs aren't working right.
You only want to use genuine Motorcraft (Beru) plugs. AC Delco are well known to blow and swell up, sometimes after only one use!
There used to be a very good sticky at the top of the forum discussing the glow plug system and how to troubleshoot it, not sure where it went.