I have an 06' 350 with a 6.0 all stock. I towed a trailer and cargo with weight around 6000 pounds and now the truck is sluggish on take off and blows out a lot of black smock. I was thinking it had something to do with the turbo but I pulled the 3" hose off both sides and I can turn the small turbo fins with no problem. The 3" hose on the passenger side has some oil residue in it and I'm not sure if that is normal. It's hard to explain with words but before all this I was hearing a low whirling noise every now and then and the truck would not have as much power (turbo problems?). If I let off the gas the noise would fade and the engine would run as normal. Any help and info would be greatly appreciated.