Sending units or wonky cluster gauges?
 

Here is what I'd like. I'd really appreciate it if someone would pull up their rear seat, insulation, and protective cover with four 10mm nuts holding it on. I got this car already messed with and I'd like to see which direction the arrow is supposed to be facing on the sending unit. I've replaced the sending unit on the left and right side of the tank with known good units, and the damn thing still runs out of gas with just under 1/8 tank of gas, and digital information center says "135 miles to empty tank." I've also noticed that when I start the car the digital clock cycles by itself and it says "Alarm System Service Required" so I know the driver information module is going bad.

So, knowing this, do you think that my DIM is causing me all this mess or do you think it's possible the sending unit is installed incorrectly (doesn't look like rocket science).

2003 Volvo S80
Front wheel drive, automatic
150K miles