97 Blazer Rough Shifting

Sometimes my transmission will shift hard and then the engine light will come on. If I keep driving it will continue to shift the same way. However, if I pull over and stop the car for more than a few minutes, and restart the engine, the transmission will start to shift properly.

Any ideas as to what is causing this?

Now here's the kicker: The problem was created by adding fuel injector cleaner to the gas tank... And after I burn all the fuel with the additive in it, plus a second regular tank of fuel, the transmission will return to 100% normal opperation.

So my question is, how does adding a fuel cleaner affect the shifting smoothness of my transmission?

Could it have anything to do with the oxygen sensor, and if so... is it the front or back sensor which affects the transmission shifting? ...Or is it something else all together?

I know it may sound crazy but the problem may be the ignition switch.

I experienced the same problem when my switch went bad several months ago. Get it scanned. Autozone will do this for free. The Codes I got were:
P0758 solenoid B,
P0753 Solenoid A,
P0785 Shift timing solenoid,
P0740 Torque converter clutch,
P1860 Transfer case contact plate D.

I was told it was the tranny but after some research i came to the conclusion it was the ignition switch (a common problem on the 97's and other models too). The problem is carbon buildup on the electrical contacts suppling power to different functions of the vehicle. Mine has been working fine since i fixed the switch

Good Luck