1) Use GL-4 75w95 grade manual transmission oil. The oil needs to be changed every 40K Kms. This should resolve the shifting issue.
2) The brakes issue is due to improper adjustment of rear drums. Please make sure that front brakes are serviced BEFORE the rear ones. While adjusting the rear drums, make sre that the wheels are not spinning completely free. They should turn for one and a half turn before coming to a stop. This will eradicate the skidding issue.
Bro change the gear oil to the above mentioned grade and you should be good. DO NOT use Suzuki gear oil as it is absolutely rubbish! (SAE80)