When I first get in my truck it wont trun over on the first try. It take about six to seven trys to finally start. I changed the fuel filter and still didn't work. The pressure gauge cap in the motor says about 50 to 55 psi. I hear the fuel pump working when the key is in the on postion.

SOURCE: 1997 GMC K1500 4x4 5.7 ex.cab SFI injection system

Did you check the fuel filter?
or possably the catalitic converter is cloged, check the exhaust pressure.

SOURCE: no power when hit the gas

The fuel presure should be at least 60- 66 psi key on engine off, and then drop some when started, if it doesn't go any higher than 50 psi that would explain your backfire concern. If it is low then the fuel pump is weak. I have also seen soot on the little wires inside the Mass Airflow Sensor cause a concern like this.

SOURCE: 2000 GMC Jimmy will not start

The oil presure switch does have some bearing on the problem but my suggestion is to change the coil. I had a the same problem with an astro van. I changed everything that you have described and it fixed the problem just for a little while and then all of a sudden did it again. I changed the coild and the cold start swithch and never had the problem again.

SOURCE: 1999 Yukon cold start problems.

1999 Yukon Start Issue - I have replaced the octopuse, battery, fuel filter, fuel pump, still having problems starting in cold weather, sometimes after a heavy rain.

Any suggestions?

Thanks

SOURCE: 2000 gmc jimmy wont start fuel pump comes on and cuts off...

When you hook the pressure test guage to shrader valve on fuel rail what it reads is what the pressure is from pump, around 60 p.s.i. all you need to do is hook up the guage and turn on key, you do not have to turn engine over, and if pump is good it will shoot up to 58 or 60 right now.