whines in gear

Hello, I recently got a 1994 4runner automatic 4wd in red, 194k miles on the clock. I have the intention of taking it off-roading and have been daily driving it for about 3 weeks, whenever I pUt it in drive or reverse, it kind of groans, the pitch goes up and down with engine rpm until its at cruising speed then kind of fades (or maybe its the rough suspension covering up the noise) I recently did a fluid change for the transmission, the fluid was real dark, almost black (i think tis original) but it dint smell burnt, its's been 3 days since the fluid change and she still goes into gear and moves. I'm almost certain the noise is the torque converter as I've seen other videos with almost the exact same noise under the exact same conditions where they replace the torque converter and that solves the issue, however my work buddy (were both diesel techs but he's been there longer than me) assures me its the pump and that ill need a whole new tranny. I figured if its the pump that the whine would be there constantly, not just in gear right? has anyone encountered this before? Do you guys think its the pump or just the torque converter? Thanks for reading!