4L60E tranny fluid blow-by issue
I noticed a new drip under the truck, today, and took a dive into it. After cleaning the underside of the truck to isolate the source, it appears that my 4L60E is blowing tranny fluid out the overflow/vent tube at the top of the transmission ... which is then all sorts of fun to find because it hits the spinning shaft and is, thus, spun/slung radially along the underside of the truck.
I've read that a common cause of this is transmission overheating -- due to hauling/towing heavy loads and/or the impact of mountainous terrain. I've not been hauling or towing anything except myself and a small backpack these last few weeks ... and I've been on mostly flat terrain, so I don't suspect I've got an overheating problem. (As I don't yet have a working trany gauge in my 04 Sierra 1500, I'm stuck with looking at driving patterns.)
I also read, today, that a common cause is overfilling the tranny fluid. So, I warmed up the truck and checked the tranny fluid level while the engine was running and found that the fluid level was just fine.
The last thing I read on the issue is that the transmission oil pump could be the culprit -- either its seals are leaking or the chamfer in the pump body rotor pocket is too large. Those mentioning this have replaced their tranny oil pumps with rebuilt pumps (and presumably new seals) .... which resolved their blow-by issues.
I'm mechanically inclined ... but I'm largely engine and tranny-stupid. I don't mind learning but I'd prefer to learn in small chunks. I'm curious how bad it is to replace a tranny oil pump. I know the tranny pan and filter must be removed. It looks like an adapter on the valve assembly (which is held in by a retaining clip) must come off and then the torque converter solenoid must be removed. At this point I think the oil pump assembly can be gently pried out and removed/replaced (in addition to replacing its gaskets/seals).
My big question is whether or not the tranny must be removed from the truck to do all of this ... or if the work can be done with the tranny in place. Please advise, as I'd like some guidance from more informed/learned transmission folk, and thanks in advance for reading.