Just a thought, I had a Tahoe that had a bad rear axle seal and it caused gear oil from the axle to leak onto the brake rotor. When I drove it it caused the gear oil to burn and burning gear oil smells more like garbage than any automotive fluid I can think of.
If it comes back maybe check your rear axle seals or for gear oil leaks anywhere, really.
1999 TJ 2.5L AX5 NP231 D35/30 4.11's
*Disclaimer - I've probably had a few beers