Picked up an '84 Chevy K30 yesterday, M1028 dually... has some interesting additions from some previous owner. One of which appeared to be a suburban or blazer fuel tank mounted under the rear of the bed. Fair to good job was done grafting a fuel door to the drivers side rear quarter. Noticed the tank was a little loose when I picked up the truck yesterday though. Today driving to my sisters after work I put some fuel in the tanks not knowing how much was in it. Front take was actually full, rear they ran the filler hose kinda poorly and it was very slow to put anything in it. Although I put enough diesel fuel treatment in it to treat 25-30 gallons before I started pumping... It was going so slow though that I stopped at 10 gallons. Got to a big hill just before my sisters place and I notice the truck loosing power, almost acting like its running out of fuel. Barely had enough power to get the truck up to the top. So I'm thinking I didn't put enough fuel in with the treatment and it's not running well because of that... went to another station and put in another 13 gallons in the rear tank, figured that should help dilute the treatment enough. After I let the truck sit for an hour at my sisters I head out again and the truck is running great for a while it seams. Stop and check the tranny fluid... add a quart then start off again... Truck starts running poorly again. Every hill I can barely keep the truck running let alone have it pull its own weight up over the hill. So I start taking back streets to stay off the main roads and avoid traffic. Most of these have small round abouts in all the unmarked intersections rather than depend on the old fasioned yeild theory. Of coarse the dual rear end likes to catch some of the curbs (ok most of the curbs in the center). I actually stopped and put on a new fuel filter I picked up earlier thinking *MAYBE* the fuel treatment just plugged up the filter?... Bleed it out, starts up and runs great again, for a couple blocks. Now back to no power, lots of smoke, sometimes I have to put it in nuetral and floor it to barely keep it running. I get small bits of power every now and then and get it moving again. Finally got on a down hill section and start going thru more roundabouts. Catch a big bump on one more and realize what is causing all my problems... About the same time I hear the rear fuel tank hit the pavement and start dragging. Aparently the previous owner had many great ideas, but unfortunatley had no clue how to make them work even remotely correct. No gas tank straps were used to support the rear tank, just the mear strength of 3 fuel lines and a filler hose (maybe the guage wiring?). So the more weight I was putting into that rear tank, the more it pulled down on the fuel lines and pinched them off starving the motor of fuel. Now your thinking why not switch to the main tank? Because I pulled all the scarey looking wiring out of the fuse box last night and must have disabled the factory tank switch cobled in under the frame. But I had my tools, and with a single flat head screwdriver I was able to swap the lines on the crossover switch and make the primary tank the default one with no power to the switch (I still need to get the fuel guages working anyway). Truck now runs normal again and made great time finishing the drive.