Doesn't Want To Start

[99SLT4.3]

A friend has an 03 Silverado EXT 4X4 5.3L with 115K. He has just replaced the fuel pressure reg., fuel filter, starter, and added fuel system cleaner trying to fix a starting problem. When he goes to start it, it just turns over, but won't start. If he places the key to the D position, drops back to the C position, then turns to start, it fires perfectly. The fuel pressure goes to 60 psi, as it should, but it doesn't hold the pressure. It begins to drop even as he's testing. WHAT GIVES? Any help would be appreciated.

[AgDoctor]

i heard of this before form a friend of mine. he had his throttle body removed and cleaned and fixed his problem. hope that helps.

[99SLT4.3]

i heard of this before form a friend of mine. he had his throttle body removed and cleaned and fixed his problem. hope that helps.

 

Thanks!