I have a 2003 Chevy ZR2 Blazer and when i get over about 40 miles per hour the service engine soon light starts flashing what could that mean

indicates faulty/injector/s
run the fault codes to find causes for faults

If the service engine soon light is flashing, it means the computer has detected an engine misfire with the potential of catalytic convertor failure. Don't just tune it up. Bring it somewhere they can read the trouble code. Sometimes it will designate which cylinder is having the problem.

have code retrieve for engine then the reduced power light is combine with pcm and ABS module

Flashing service engine lights are very bad, means there is a problem that can potential cause harm to the engine. Sounds like you may have a bad coil. Take it to a place like Autozone which can check the check engine light. They'll give you a print out that will give you a better idea on what's going on. If it's a misfire on a cylinder or two, check plugs and coil, also could be an injector.

You will not be able to go any faster when the engine light is flashing the computer of the vehicle has gone into protection mode.It will not allow it to go any faster. When the light is flashing it means their is a potential danger of damage to the engine or transmission and the computer goes into protection mode.You must take it to a garage and get the computer scanned and the repairs made and the computer reset after the repairs are made. Do not drive this vehicle at all it would be safer to have it towed so you don't cause more damage to it

have a trans shop check the linkages/sensor should be cheap unless linkage is damaged from 4wheelin
Good Luck

Fuel filter plugged.

swng,
1) Is the service engine soon light ever on when engine is running?
2) Per your description I would look at the ECT sending unit. It sends coolant temperature information the the Engine Control Module for proper fuel delivery for cold engine start. It may have lost its calibration.
Let me know.
Regards,

Wow, I just went through the same problem and guess what it was a clogged converter and a bad oxyegen sensor. The garaged fixed it up for me by putting an eco converter on it and a new O2 sensor. I have a 2003 Chevy Impala,V6 3.8 engine. Good Luck!!!!

you have a trouble code stored. This means the pcm has detected a problem somewhere