What Gear Ratio at the rear would be good in this truck?

I have a 1988 Ford F350 2wd that had the 7.3 Intertrashional Diesel in it with an automatic C6 trans.  I swapped the motor and trans out for a 1993 Cummins intercooled 12V with a Gutrag 360 5 speed trans.  The truck is up running and driving, although it is ENTIRELY TOO torquey.  My truck tops out around 60MPH.  The current Rear Ratio is believed to be a 4:11.  I pull a light trailed about 4 to 5 times a year, and I personally dont care if the truck is a bit sluggish accelerating with a load.  I do drive the truck a lot.  like 3 to 4K miles a month mostly highway and no major load.  I would like to idealy have a 90MPH or higher top speed.

The gear ratios in the trans are as follows: For first gear through fifth gear respectively, the gear ratios are 5.53:1, 3.02:1, 1.60:1, 1.00:1 and 0.77:1.

I was wondering if I would be better with a 3:55, 3:73 or if I could go as high as a 3:08?

The motor is not modified, and is all stock settings, the pump is not even turned up as of yet.