Well I found an NV3500 for my 96 dodge 1500 truck...my question is, the "specially formulated" Mopar Manual Transmission Fluid runs about $20 a quart...is there a suitable substitiute for these things?

I have heard some say ATF, some say 90wt gear oil...I dont want to ruin this thing. Is the $20/qt stuff necessary?

BTW: I plan on replacing the rear seal, from seal, and front bearing (throw out bearing I guess), and get a new clutch as long as I have the old one out.