Grinding when shifting from 3rd to 4th

I am new to stangnet and this probably has come up before but I have a 03 gt 5 speed when I’m shifting from 3rd to 4th it grinds on engagement. I was wondering if there is an additive or something that would help out with this issue. Maybe buy me some time to save up some money to replace the synchros (I’m sure that’s the issue)
 
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