When I start my 1999 GMC JIMMY sometimes it starts right up. Sometimes its as if it does not get enough fuel then it starts. I have been told it could be the fuel pump or the fuel injection regulator. Which could it be?

I been having fuel injection troubles myself and seems to me your problem may be your fuel injection pressure regulator,before starting when you turn the key so your dash lights show up and at that same time you should also hear your fuel pump motor spinning which means that its working and sending fuel through so you may have a fault with your regulator,,hope that helps,goodluck.