Hello there! Is there a way to get the gold medal or is it one more bugged mission? 'Cause no matter what I do, I'm not able to get all the points needed for it
Can't remember what this specific service was like, but make sure you follow the 15mph speed limit in the yard. You can only go up to 15.4mph in this case. Even 15.5mph will be counted as speeding. If you still can't get enough points for gold, then the scoring in this service must be broken, just like many other ones.
One way I have got Gold on other services, is just to keep running up and down the yard road and building "Running under speed" points. OK its very boring but you can get there. Check how many points you require and then check how many you get for finishing the module. Then just do a hundred points more just for good luck. I have done it twice now on two "Trans Pennie" modules that I could never got to Gold on.
Sand Patch is a very old route, and at one time DTG opined that some short services just weren't "worth" a gold medal, so silver is the best you can get.
I just did this one again the other day and got a score of 7600, which is the exact score needed for gold. Possibly speeding might be the issue as HaibaraHariko suggested? If scoring is that tight, one 15-point dock would put you back to silver. The only SPG services I've been unable to get gold on are U876-B (coal loading, bronze) and U876-C (runaround, silver), but a quick search will show that those are typical results for everyone.