t444e code, needs more power

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I have an IHC 4700 box truck with a t444e and Allison auto. I have retrieved a fault code of 313. Anyone know what this is and what needs to be done? Also, it has a 70mph speed limiter and loses 10-15 mph up hills. Is this normal? I am considering performance upgrades, maybe a chip, although it seems they are no more than a 10k or 14k resistor that changes the ICP signal(can't you get resistors for less than a buck at Radio Shack???). But I haven't seen anyone address exhaust on the bigger trucks. Anyone tried to put a less restrictive exhaust on one of these? The down pipe is only 3 1/2" and that muffler is huge and surely very restrictive. I would think a bigger down pipe, if available, and a free flowing muffler of some type would allow the turbo to spool up quicker and cool down the EGTs. I know the bigger exhaust works well on the F350s. Anyone have any thoughts on this? Has anyone used the factory DVD repair manual?

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Now I also have a code of 333 and the engine warning light comes on after driving sometimes 100 miles sometimes after 250 miles. The fuel filter light also flickers on occasion. I had the filter changed about 10 days ago and again today. When I turn the engine off, it will start and run OK again for a while. Anybody? Andybody? Bueller?