if its comming into the cab, then yes Id bet on the upper plugs. Get a mirror and look up there to verify. you can pull the shifter and its associated rubber covers off. If it just started you might be ok. get the fluid level checked ASAP. I bought my truck, someone had let the plugs leak, plugged them with RTV and it burned up the mainshaft and 1st gear. Thjats probably why they sold it. Anyhow $900 for a rebuild, new clutch kit, slave and master cyl's I had the plastic plugs replaced with the steel ones. Bad point is you have to pull the trans to get this fix.