sensors

check fuel pressure may be low. auto parts rent gauge

I was looking at my exhaust today and I saw that their was not a Cadillac converter on it and I found an exhaust leak in front of where the cadilac converter would be would that cause problems?

It may cause the lean code, but normally that code would be a 420, but with a missing converter it's hard telling what code will pop up. Check fuel pressure

I could not find the place to connect the fuel pressure gauge too , but when I got the truck the guy told me he put bigger injectors in it , a guy told me by doing that it could mess up the computer and make the o2 sensors read bad is this true?

there shold be a connection on fuel rail for gauge, putting larger injectors will make it rich you have to do the basics which include checking fuel pressure but with converter gone all O2 sensors are not going to read right. see if you have a vacuum leak. check hoses etc. you shold have non exhaust leaks but with the way this truck is I don't think you can do much with it.

I changed the o2 Senors and it fixed the problem thanks I have another problem it is throwing code po 720 which is for the speed sensor I changed it and it didn't help at all what should I check next?

follow instruction on pic. you willnot be able to do anything that says to use a scan tool because it take a pro model to do that.