Hello guys, I have a transmission fault I'm trying to diagnose. Only Error code is p0741

Truck is a 2005 LR3 SE 4.0 v6, 150k miles

I bought the truck 3 months ago, drove truck home approx 200 miles no issues as soon as a got home the transmission fault appeared, drove truck for couple weeks without any codes or transmission faults, by week 3 got on freeway and drove for approx 45 min at 70mph, got to the mountains and approx 5 miles going up the transmission fault pop up, drove it like that for approx 120 miles, after that every time I hit 63/65mph the transmission fault comes on. Took it for transmission service and still doing the same at 63/65 mph transmission fault pops up

any help will be appreciated

 

That error indicate a slippage difference within the transmission. This could just mean its low on oil or needs a change.
Just reread and you indicate it was serviced, could try a tube of 'Dr Tranny'

 

added a tube of Dr Tranny, did not help still doing the same transmission fault at 65mph