Ford F-150 - 1997-2003 :: Crank And Not Start Or Sometimes Would Start

I have a 97 F150 w 4.6L engine with auto trans which I bought new and has approx. 150,000 miles on it. Very recently it would crank and crank and not start or sometimes would start. In searching through multiple threads on here many of the Ford techs recommended replacing the IAC valve as a cheap and easy to do fix and I did that. The OEM factory IAC valve appeared to be dirty with black soot. I also cleaned the MAF sensor in the air filter snorkel. I also replaced my very old battery at the same time. I verified that the fuel pump was running for about a second or two and shuts off after the ignition switch was turned to ON so the fuel pump is running since I could hear it. I replaced he fuel filter several years ago so it should be OK and not plugged.

I had to use starting fluid after the battery replacement to get the truck running but after I got it started and I did several driving cycles over three days to make sure the truck computer reset properly and the truck was running fine and starting without a problem. I was checking the starting every 4 hours or so for the first two days and it would start on the first crank every time without a hiccup.

This morning on day 4 when I went to start it the same problem occurred where it would crank several times and not start. I loosened the filter snorkel up and shot some starting fluid in there and it cranked up after a couple of tries and ran fine all the way to work. It seems like I have a fuel delivery issue of some type. I know the fuel pump is inside the tank and very expensive to replace if it turns out that it needs replacement. That is definitely beyond my capabilities. I plan to check the fuel pressure this weekend when I have a chance and can rent a gauge from Autozone.

My question is this: If it turns out to be a defective fuel pump can I just add an inline electric fuel pump outside the tank and have it pull through the tank in the pump leaving the in-tank pump abandoned in place? Are there any other sensors or parts I should be checking for voltages, resistance, etc. that would affect fuel delivery for starting? The truck seems to run very well with no misses of any kind and accelerates nicely after it starts. Also, no "Check Engine" light at any time and the bulb is working since it lights up momentarily when the ignition is turned to ON position.

Update Saturday June 25 - Got a fuel pressure test gauge and got the following results after installing a new fuel filter:
1. Bled off fuel pressure to connect gauge and after 5 or 6 Key On, engine off cycles the pressure came up to about 38psi and truck started up fine after pressure was at 38 psi. The pressure built up slowly after the bleed off with each ON/Off cycle and that is why it required 5 or 6 cycles to reach 38 psi.
2. Key ON, engine idling maintained 31 psi
3. Key ON, engine revved up slightly maintained about 31 psi and seemed to stay there even with more throttle increase.
4. Key ON, engine idling, disconnected fuel pressure regulator line and pressure increased to about 40 psi and stayed there
5 . Left the gauge connected after turning off engine. Key OFF, engine off, after 1 min fuel pressure increased to 33psi. It is about 90 degrees in the shade here today.
6 Key OFF, engine OFF, after 2 min gauge read 33 psi, after 5 min increased to 34 psi, after 15 min decreased to 33 psi, after 30 min decreased to 29 psi, after 45 min decreased to 26 psi, and after 60 min decreased to 23 psi. The pressure seems to decrease slightly with time which I think is what it is supposed to do. Is the pressure decrease rate too fast or about right?

The truck seems to be running fine and starts up immediately after sitting for a few hours but I am making sure to turn the key on/off for at least one or two cycles to build up fuel pressure and the truck starts every time for the last week. Does it seem like my fuel pump is OK or not? Fuel pressure regulator OK or not? Any other diagnostic tests I should run?