Troubleshooting what I think is limp mode

[Bigcountry]

I have a 94 Nissan Pathfinder xe-v6, 5 speed 4x4, it has no error codes, it flashes 55, the truck cranks and ideles great when you try to accelerate at about 21 to 2200 rpms the vehicle stalls and does not recover until it gets to 1000 rpm's it feels like someone turns off the ignition switch,

it does not matter what gear I'm in or in neutral, I can drive it I have to baby it and top speed is around 45 miles per hour! While trying to troubleshoot I unplug the TPS sincer and to my surprise it runs like a bat out of hell but the check engine light comes on and throws a GPS which code and also it idols rough and will not pass inspection , and the gas mileage gets even worse which if you have one you already know the gas mileage is not very good, I have changed quite a few parts sensors and switches to try to fix this problem

can you any one help please