cat c-15 mxs

bought a 2006 t2000 with a c15 mxs 435 to pull containers,i don't know whats been done to it as far as mods and judging from the fuel filters yes im finding out i bought someone else's problems, question is is that the fuel filters that were on it were the cheap luber finer, dont remember the part # for the secondary, switched it out for a cat filter ran fine for around 5k, so before doing a little research, i replaced the LFF5 on the primary still runs like crap,i would like to go with a different primary but not sure which to use, i had a friend go to get a primary fuel filter for my motor because i was running and couldnt get to cat house and they gave him a element 9m-2342 for the case as fuel filter, well $230 to swap out to that set up is just to much at this time, i keep reading cat filters (what do i run for the primary water separator) is the way to go and then fs 1212 works well for some, i just would like more than 4.5 mpgs loaded and good god the lobbing of the motor likes its starving to stop, the second problem im also having is the speedo started jumping anywhere from 5-15mph with no change in speed since the filters started giving me problems....thanks in advance for any input

 

Well a tune up, overhead may be in order....whats the going rate for that, or better any recommend shops in around Houston, I had I guy look at it, he owns seven trucks does his own work, he stuck his had on my blowby tube had me rev the motor up then took he's hand off after I shut it down, lots of air blowing back, he seems to think its my rings,but I'm losing no oil or gaining any for that matter,the other problem I have is he owns 7 trucks and my be trying to get me to get the work done to put me in one of his trucks,paranoid perhaps....staying tuned....