Being caused most likely from your network connection.
Solution: Go in game and type; /netstats. If you find packetloss, restart the router. If the problem continues, wait for approximately two days. If the problem continues aswell after the two days, contact your ISP (Internet Service Provider) and inform them about the issue. If they don't find a solution, change your ISP.
Problem number 2:
You're really far from the server host.
Solution: Move closer to the server host in order to get a better ping and play better.
There are 2 main causes of lagging.
1) FPS lag. If you have any modifications like gun mods, skin mods, cars mods that you have added recently, remove them.Try to play on a clean GTA and see if it solves the lag issue.
2) Lag caused due to internet connection: Check your net connection, See if you are having packetlosses (Press f5 In-Game) See if restarting your modem and PC fixes the issue. If the problem persists, change your ISP or upgrade your net plan
There is one other cause of lag which is when there is a server sided lag, but since no one else is facing this problem, hence its client sided. Hope this fixes your lag issue..
If you need anything else please don't hesitate to make another question or send me a private message. - Question Answered, moved to answered section.