My budget's around RM2000
I play hard rock especially, though heavy metal comes in second. I'd like to play Guns N' Roses, Led Zeppelin and having a Metallica sound is also nice. Getting to sound like Slash on his November Rain solo would be awesome
I'm open to both new and used amps.
I need a good gigging amp and preferably solid state as my city here doesn't seem to offer any valve amps (I've been to 3 music stores and the only marshalls they sell are the MG series @.@)
I'm located at Kota Kinabalu, Sabah, Malaysia
Now I'm using an Epiphone SG Special and Beta Alvin BM6 amp

This amp will be my primary gigging amp from now on and it will be my only gigging amp for the next ten years (I'm only a student haha). So I need to be absolutely sure that the amp I buy will make me happy for years to come. So far I've been looking into the Peavey Vypyr 75. I haven't looked into the Roland Cubes yet. Any suggestions?

I've heard that the Vypyrs have a lot of reliability problems and you need a patch to fix it. I don't have a reliable store anywhere here (I asked a salesgirl to find me a Peavey Vypyr and she gave me another Peavey which wasn't from the Vypyr series and I asked another salesgirl about the wattage of the Marshall MG30CFX and she told me it was 70) WTH? hahaha seriously true. So I'm afraid they won't know a thing about this patch.

Please help me cuz now my amp sounds terrible. It has terrible terrible sustain even though my gain is around 7. I appreaciate any help and thanks in advance.
First off, don't get too hung up on the wattage. In my experience, wherever you go to gig, they will have a PA, and you will be micing the amp (or putting a microphone in front of the speaker). I don't know if that's true in your country, though.
As long as you can hear it over the drums at practice, you should be able to gig with it.
That said, the Vypers are super popular and usually pretty good as modeling amps go. This is especially true for metal tones. The 75 would be plenty. I haven't heard too much about reliability, but I don't own one.
Harmony: Stratocaster
Alvarez: F-200
Schecter: Omen 6
Fender: BXR-60
Dean: Metalman Z Bass (Betty)
Egnator: Tweaker 15
Pearl: Maximum
Custom: Harley Quinn Bass
Custom: TK-421 Explorer
A steadily growing supply of pedals
A local gigging pro that I know uses a Fender Champ X2 combo amp. He swapped out the stock Fender speaker for a good quality 10" and says it covers all the sounds he needs for his gigs. I am not sure whether this amp lends itself to the style of music you play, but my friend says the reliability/durability of the this amp is excellent.