My eaton fuller transmission wont shift past 5th when it tries to get into 6th gear it just makes a grinding noise

SOURCE: popping or grinding noise when placed in reverse

check the rear dif.

SOURCE: NO 5TH GEAR IN MY 1995 MITS 3000,NO NOISE,NO PROBLEMS SHIFTING

I have the same problem. on the passenger side under the fender you will have access to the transmission. Remove the cap on the end. You will need to drain the transmission fluid and replace all the gears in the end cap if damaged hopefully they are not and you can just tighten up the nut. What happens is a nut comes loose and backs off the pressure on the bearings and you loose 5th. I removed the entire transmission and opened it up. There is nothing wrong with the other gears, because your problem is with the 5th gear synchronizer assembly. I let mine go too long and I'm having to replace everything. Make sure you put the appropriate torque on the nut and hit it with a hammer to lock it down. This should really be designed with a different method of keeping that nut in place. It's costing me lots of time and now money at the stealership. Good LUCK.

SOURCE: I'm just a girl. 99 suzuki esteem 1.8L wagon wont

Did you check the oil level inside the gear box? Most people never service the car, so this part gets neglected. if it ran out of oil, you probaply broke it(a big repair bill).
Try putting oil(probably 90w gear oil;check a manual,internet to make sure;if you make a mistake dont worry any oil is better than NO oil).
Check the differential fluid level too;same thing will happen if you neglect doing this.

SOURCE: ford fiesta 1999: trouble shifting into 5th gear

gear linkage worn joints.

SOURCE: VW GOLF 1.4 1999 S. Gearbox makes whining sound at idle

No good news on this one I think
Your whining sound problem is the Layshaft bearings in the gearbox are badly worn. It also seems that the baulk rings are damaged on 5th gear.
John