Ok my 02 ranger says 5w-20 on the cap, but my owners manual says 5w20, 5w-30. Is it ok to use 5w-30 in it? Both oils have to same cold flow characteristics dont they? I use full synthetic and am considering switching to 5w-30 simply because no one makes a 5w-20 full synthetic high mileage.

 

I'm sticking with Mobile 1 5w-20.
The main reason is the cam syncro assembly which drives the oil pump. I changed mine out before the bearing got too bad. The bottom bearing is splash lubricated through a hole that is only around 2mm diameter. Too heavy an oil won't flow enough to keep the bearing lubed. Result is an oil starved engine when the pump drive quits.

 

x2 on Mobile 1 5-20; my 3.0L has known no other.

Not sure about your truck but both my 5.0L and the 2.3L got noisy when 10-30 was used but 5-30 not sure.
Try it and if the rockers get loud then change to 5-20.

IMHO...Stick to 5-20W unless you have unusual situation for heavier weight oil.

 

you can use 5w30...it is just a little thicker than 5w20 when up to temperature. same flow at low temps, thicker at high.

Valvoline's MaxLife does come in a 5w20, you might have to see if your parts store will order some in special for you. My '98 is backspec'd to 5w20...but since I'm on track for only 7k miles per year...it is going to take me a while till my next change.
Advance Auto Parts: MaxLife 5W-20 Synthetic Blend Motor Oil (1 qt.) by MaxLife - Part VV169
I know my Advance does not have that readily on the shelves...but I'm sure they could get my order in within a few days.

Oh, and Castrol makes a 5w20 high mileage oil as well.