2017 ford e450 6.8 super duty will not start.

[Russellrer]

I have a 2017 ford e450 6.8 super duty chassis, it has a Jayco RedHawk right built on it, bought it three years old, never had a problem with it, when I’m not using it I start it ounce a month and run it for an hour or so. Now my problem, I went out to start it up and battery totally dead, tried to charge it, could only get up to 8 and a half volts. I went and purchased a brand new Die Hard battery, checked and cleaned both poses and battery cables, went to start it, all it would is make a bump to start two times while holding the key, it would not start, after trying, I don’t know how many times it would start and run for about five seconds. Now it has only done that about three times, I was researching other forums and have made a few change outs, now the code I did get off the vehicle was a P0607. What I changed out was the starter, fuel control module, ignition switch, used a contact spray on the main control module connections I also cleaned a number of ground connection points. I tried some starting fluid to see if it would start, no go. With all the computer controls, the things I haven’t changed is the in tank fuel pump and main control module, also after it fails to start the parking P light blinks. I’m 78 and am limited on some things I can do, I want to check the fuel tank pressure but can’t locate a fitting to use on this e450 as it has no Schrader connection point, any help will be appreciated please.