'99 4.3 V6 questions

[53burb]

I have a '99 Chevy (NBS) 1/2 ton Silverado 4x4 with the 4.3 engine & manual tranny. The truck has 130000 miles.
Recently, as of about a month or so ago, the truck stopped starting with just a turn of the key. It turns over a few times before it starts. It only does this when it is cold.
Yesterday, I changed the spark plugs, wires, air filter, PCV valve, cleaned the MAF sensor, new cap & rotor, & changed the fuel filter.
It is still the same.
My next guess is possibly dirty injectors or a weak fuel pump, or maybe weak starter. The fuel pump was replaced with a Delphi unit at approx. 105-110000 miles. It's noisy, but it has been this way for awhile. It also had the "check engine" light on. I disconnected the battery while I was changing everything, so that "check engine" light is now gone, but I'm sure it will reappear. I had it checked before & IIRC, it said one of the banks was the culprit.
So my questions are: what is a good brand of fuel injector cleaner & can the timing be set on this engine, or does the distributor only have to be installed correctly & the computer controls the timing?
I don't have a gauge to test the fuel pressure.
Any other suggestions?

Thanks,
Chris