Need Fuel Pressure Testing Help 2007 5.7L

Tundra 2007 4X4, 5.7 L. Code P0305 misfire on cyc. #4 & 5 while pulling boat trailer, car shuttered, Check Engine, SVC Off, 4Lo lights all illuminated (vehicle was not in 4Lo). Since there was 86,000+ miles on truck and noting last forever, I pulled and replaced all coils and plugs with Denso brand. Noticed old #4 plug had insulation damage at electrode. All Cylinders at 77+/- PSI. Test drove all normal until rapid load placed on engine at 5K RPM, then car shutters, Check Engine, SVC Off, 4Lo lights all illuminated again. Thought it might be a fuel injector on #5, so I moved injector to another cylinder, problem did not follow. Turning off engine and restarting, engine runs fine until rapid load placed on it again. Wanted to check fuel pressure but found no Schrader valve on fuel bar. I rented a fuel pressure test kit and tried to connect with Tee/Schrader valve at fuel feed line but T on test kit smaller dia. then Toyota fuel line connector so no go. Is there a specific fuel pressure test kit that works with this engine or a another way to test fuel pressure. Or should I be looking for another potential malfunction causing this problem with engine under load?

 

Have you gotten anywhere on this problem? I'm getting code P0138 which has to do with the downstream O2 sensor and too rich coming through the exhaust, but it is not the O2 sensor.

So I'm looking at fuel pressure and was going to go get a test kit from Oreillys, but sounds like there might be an issue with testing the fuel pressure from your post.