Eaton rear differential question

[G-749]

Hello all, 1970 C 20 Longhorn Eaton question , 89k showing on odometer, 1400+ since I bought truck, already towed 3800 lb double brake axle 28ft dove tail trailer empty , going to put 4200 lb Kubota
grapple n scrape blade on it . Put truck on jack stands , changed engine oil again, 20W 50
Valvoline , 3 qts Royal Purple 75 140 w synthetic in rear end , while on jack stands , I counted tire revolution to driveshaft revolutions , almost 5, prolly 4:57 . Here is question, rotating wheel on either side forward makes opposit wheel turn in reverse , when turning either wheel in Reverse , both wheels rotate in same direction , truck under power spins both wheels on pavement or gravel , SPID missing, 700R4 tranny works awesome under power and part throttle shifts , will change 3 gears before clearing intersection, looked thru search , about this , lots of info but nothing specific about this , pinion seal small leak , only got 2 qts out of it , no small tag on diff cover, diff has been opened, and RTV sealed by PO
Do I have a G 86 No Spin Axle based on what I have described? Inquiring mind wants to know what others think about this. Any and all thoughts , comments, input welcome .
Good luck on all your projects!!!