I would not worry about the rod bearings yet.
Like DarylJ said it is a real PIA to get to them.
Just change the oil and put in the Castrol Syntec 20w-50 and drive it and see what happens, if and only if the oil light comes back on at a hot idle would I spend the time and money to check the rod bearings.

Remeber that the things that heat up the internal temps of a engine are extended high speed driving, towing a trailer, off roading and sitting in heavy traffic for a long time.
So...if you are doing any 2 of those things on a regular basis then you need to use the correct oil and change it at the correct times.
For you, once you start using full synthetic motor oil I would change it at 3,000 miles for the next 2 oil changes and then switch to 5,000 mile oil changes and do not go any longer than 5,000 miles and stay with the full synthetic 20w-50.
I think this engine is going to be fine, it wont last you 200,000 miles, but I think you'll see well into the 100k's with it before it needs any major work.

 

I will do precisely that SPIKE. Thank You very Much.

Light went on ( all 4 times ) right after a Hard acceleratión or High RPM.

I use my disco , Only about every 2 weeks and that is highway use and off road .. practically never in city or heavy traffic.

 

Yup sounds like low oil psi from the high crankcase temps...coming off a long highway cruise at high speed and then slowing down for a exit ramp and then the oil light come on right?
The full synthetic 20w-50 should cure that straight away.

 

Hi There Spike..Itīs My second computer in 2 months Ive been having bad Luck with viruses ( as well as my Disco ) Took It to a LR shop were they told me It had a BAd IAC Valve and that was causing My oil Light to come One .. My Idel rpmīs are about 700 or 7500 and I also shot my ABS Computer and cant engage the CDL now. Seems My old work shop ruined my Truck I alrready sewed the hell Out of them But Now I dont know what to do .. Iīve been Thinking of selling.