Listen to the above posts. Before you go spending all that tax refund, get a monitor solution!! You may just find out that you'll need the cash to fix issues with your truck.
As mentioned already, either a Edge Insight CS/CTS (monitor only) with the capability to read Fuel psi and EGT. Or the ScangaugeII with separate EGT/Fuel psi gauges.
You need to check the health of your motor first. This link will help you understand some of the issues.
Things to consider about owning a 6.0L
Now, since the Edge Insight CS/CTS and ScangaugeII is only for monitoring, the best tuner for the 6.0 is a SCT with custom tunes. Sure you could go with the SCT Livewire or TSX, as a monitor and gauges in one package, but most who have used them, don't like the monitoring capabilities of them. The Edge Insight CS/CTS will monitor so much more.
With that said, most prefer the Edge Insight CS/CTS or ScangaugeII for monitoring and the SCT X-3 with custom tunes for a programmer.
Since you are experiencing issues with the degas bottle, it could be just the cap, or overfilled the coolant, or failed EGR/oil coolers, or headgasket failure. You really won't know until you have everything tested and monitored.
Stick around and start researching and reading up before you go spending money.
2004 F350 CC DRW King Ranch
X-3 tunes by DJ'S,QT,GH,ID. Gryphon FICM tunes, ARP studs,Stage 1turbo,ATS coolant recirc lines,Swamp's 48v ficm,coolant filter,AD2,Snow Perf stage II,EGR delete,4" turbo back straight pipe,S&Bintake,Quad "A" pillar autometer gauges,Suncoast Tri Disk Conv.,Billet input shaft,Suncoast superduty rebuild kit,Trans-go shift kit,Mag-Hytec trans pan,CFM+ elbow,ccv mod,15K reese 5er,17" LCD TV/DVD,Cobra 29 Nitewatch CB