Engine light comes on after 45 mph

Maybe have a fuel pressure test done sounds like the fuel pump may be going.

P0340 code means "Something" is wrong in the timing...
from CMP (Camshaft Position sensor) to the crankshaft bolt.

Very first thing, verify connectors are clean and shiny.
clear all codes, even hard codes.

Is the check engine light on ? How does it run now that it has cooled off ?

The first thing that comes to my mind is "45 MPH"... and let me explain why.....

Your engine you said is running GREAT so a MPH is not going to effect the running of the Car but what happens @ 45 MPH you ask?

Your Torque Converter goes into Lock up.... If the Torque Converter is slipping in and out of lock up, you are going to have an irregular pulsating of the engine playing catch up.

you need to do this, try and drive the vehicle (you did not say what kind of vehicle it is), and drive it without the OVERDRIVE On...

So drive it and see if it is RPM RELATED. If there is no CHUG and you can go all the way to 55-60 without issue, Slow down below 45 and put the OD IN and accellerate and see what happens..

Is the Problem SPEED RELATED? Is it RPM Related?

If it does not happen with it OUT of OD, then what you probably have is a Torque Converter Failing...

I hope this helps

You have or had a check light on

Why have you not checked for codes &
had a repair shop diagnose & resolve ?

I would start looking for a vacuum leak. Check all the vacuum lines for cracks or breakage. Spray penetrating fluid on them until you hear the engine start to stumble then focus the spray on that area until you are able to pinpoint the location of the leak. Best of luck,my friend, Dana

At 45 or 50 is the engine RPM normal? If its higher that it should be transmission could be slipping.
If the engine is misfiring at 45 or 50 it could be the spark plugs.
If its just holding back on power it could be catylitic convertor, or possibly fuel filter.

o.k... question... when you punch it... does the car barely go... and the engine reve up? if you gently press the gas... does is act the way it's suppose to? if that's what you have... change out the fuel pressure regulator... and the fuel injector... see if that doesn't work for you... o.k... good luck to you

this sounds like is a lost joint in the engine or a broken gear box

remove the front 02sensor and drive the car like that, remove means complety take it apart from exaust, if problem goes away or gets so much better then your catalitic converter at the exaust is restricted and need a new one