So I have had this issue for a little bit. I have the fpr just before maxed out don't want coil bind. in the morning it is cooler and it starts and usually runs at 22psi but slowly drops sometimes .5 to 1psi. Then by afternoon it is high 80's to 90's out and it will start at 20.5 to 21psi, then drop as low at 20psi. So I can have it drop 2 psi. In the winter I have seen as much as 23psi when in the 60's or below. I am wondering if this is normal, I have a fuel pressure gauge in the truck. I have the red spring 18-22psi with the tpi pump, stock fuel lines, 65pph cop car injectors. I replaced the diaphragm about 2 years ago with a acdelco rebuild kit. The fpr I have made adjustable. The fuel stays solid thru rpm just seems outside temp makes it change. I just replaced the fuel filter about a month ago.
Is it possible the spring(2yrs old) is worn out?
Is it possible the diaphragm is not up to par? it is acdelco, what are others using, I have seen jet and a few other make replacements are these worth it?
do the stock tbi fpr just suck and I need to go with external vfpr?

any thoughts?
as always thanks for any input