I have owned one of these trucks since I bought it new in August of 1988. I just got rid of it 3 months ago. The salt finally did it in. Not bad for 32 years. It had over 250,000 miles on it and I changed the cooler lines 3 times because they where leaking. I changed ALL of the rubber lines on it about every 4 years ,the same with tires.
My '90 got a frame up about 10 years ago and it lost a cooler hose in the dead of winter when it was 20 degrees out and pumped all of the oil out in under 30 seconds. I got lucky and was able to shut it down in the driveway, but I had to lay under the truck in a snow storm at 2:00 in the morning to change it.
My '98 Suburban had over 250,000 miles on it when I bought it and the lines where leaking. One of the first repairs was to replace the cooler lines.
I have replaced more of these lines AND the quick connect fittings than I care to remember when I was a GM service tech. I guess my point is just because you can or have run them for a couple hundred thousand miles does not mean they are not going to fail, when they do fail it can cause major engine damage especially if it happens at highway speeds.
The after market braided hoses are made from much higher quality materials that are designed to resist heat and pressure with thicker walls and reinforcing braiding. Also the fittings are machined from much thicker metal and the have both internal and external threads to prevent failure at the fittings.
If you are happy running a rubber hose that is seeping go for it,it is your truck but don't think for one minute that the "factory" hoses come any where near the quality of a after market braided hose.