Blinking SES light
 

Alright, 04 Blazer. Whenever at highway speeds accelerating with RPMs up over 3k, the SES light will start flashing, once the RPMs drop back down to normal rate (2200) it stops. I have no misfire codes for any cylinders so that doesnt tell me anything. I have also replaced plugs, wires, cap, and rotor a couple months ago and it did it then too. Doesnt happen often just concerning when it does.

Easy Fix... Crankshaft positioning Sensor... Code P306?... 'general misfire'... but it's a false positive DTC the CPS sends... Word of Warning... DO NOT buy a 15-20$ replacement off eBay... Make damn sure you buy the $70 one from your local parts store... Also A good Idea to buy the $5 set of shims in case you need them...

I don't have any codes though, the SES light is off. Its only at highway speeds accelerating with RPMs up over 3k, the SES light will start flashing. No codes are given.

If you have a flashing SES light, then you have set a code. I'm sorry but you need to either get a better scanner, or learn to use the one that you have. I don't know which one is actually your problem, but this diagnosis can't go forward otherwise.

It does sound like a P030x misfire detection code. P0300 is the random misfire code. P0301-P0306 are for misfires on specific cylinders.

Don't replace or disturb the crank sensor unless you are planning to do a crank sensor relearn. Misfire detection will not work properly, and you will probably be setting false codes. This could be your problem right now. Crank sensors are almost always blamed and are seldom the problem.

Also bearing clearance problems can cause false misfire codes. I know this from my own experience. Do you have any knocks?

First you need to be able to read the codes. Then you need to be able to monitor the live misfire counters. If you commit to doing this, then we should be able to help you.

If your scanner won't do it - get Car Gauge Pro for Android ($8.95 but harder to use) or Dash Command for Android ($10 + $10 for extended PIDs for each vehicle) and BAFX Bluetooth OBD2 adapter from Amazon ($22) for either software. Will do most all that you will ever need on your Blazer and even cam sensor retard, but won't do crank sensor relearn. There is no cheap solution for that ($350+).