question with check engine light

Hey guys, need some advice what you think the issue could be. A while back, I had an issue with my truck stalled on me. I checked my filter and it was caked with black slimmy stuff. Figured out it had that bacteria in it as I had the problem a long time ago on another truck. Anyway, I put the killem biocide in there at the suggested dosage to kill the bacteria. It seems to have done the trick but about 2 weeks ago the check engine (yellow) light comes on. But as soon as you get the rpm's above about 1400, it will go out. Then as soon as it falls back below it comes back on again. I have changed my main filter about 10 times and it seems to be pretty clean right now. I also check and put a new filter in the fuel pump as well. Still the light comes on. Any suggestions as to why it could still be coming on? Its a 99 International 8100 with the Cummins M11.