I recently returned from Islamabad by car two days back from attending a family wedding.
All my trips to and from Islamabad have been attempted in two days leaving very little time to explore the surroundings.
My last trip from Karachi to Islamabad took me through Mail Igraveyard which was interesting.
Its a comfortable 2 hours journey on the Indus hwy and then connects back onto N5.
With the horrible road conditions in Sindh with all the road construction and diversions you should try to make Rahim Yar Khan at the least where you will find Farhan Hotel not too far in the city from the main hwy.
While driving through Sindh a great place to stop for lunch or tea is the Taj Restaurant next to Shell pump on your Right hand side of the road just as you pass Moro. Prices are very economical.
Once you reach R Y Khan you will also find a large Daewoo Stop on the right hand side which is great for food and a nice decent place to stop.
Since you have been on this rout you will know of many stops along the way but one stop you can make is Uch Sharif which is 80 kms after RY Khan and not too far off from the main hwy. The Shrine of Uch should be a great site to visit i think although i have not been there yet myself.
If you wait a few days you may begin seeing responses and suggestions from other PakWheelers.
But do share your experience when you retur.