New Index on table cause table to be locked really often

Here are my tables :

CREATE TABLE [dbo].[Trackers] (
    [IdTracker]             INT           IDENTITY (1, 1) NOT NULL,
    [IMEI]                  NVARCHAR (16) NULL,
    [CreationDate]          DATETIME      NULL,
    [SuppressionDate]       DATETIME      NULL,
    [LastUpdateDate]        DATETIME      NULL,
    [BuyDate]               DATETIME      NOT NULL,
    [Status]                INT           NOT NULL,
    [LastTrackerUpdateDate] DATETIME      NULL,
    [IdLastTrackerPosition] INT           NULL,
    PRIMARY KEY CLUSTERED ([IdTracker] ASC)
);


CREATE TABLE [dbo].[TrackerPositions] (
    [IdTrackerPosition] INT               IDENTITY (1, 1) NOT NULL,
    [TrackerId]         INT               NOT NULL,
    [Position]          [sys].[geography] NULL,
    [Date]              DATETIME          NOT NULL,
    [Speed]             REAL              NULL,
    [NbSatellites]      TINYINT           NULL,
    [Direction]         REAL              NULL,
    [HDOP]              REAL              NULL,
    PRIMARY KEY CLUSTERED ([IdTrackerPosition] ASC),
    CONSTRAINT [TrackerTrackerPosition] FOREIGN KEY ([TrackerId]) REFERENCES [dbo].     [Trackers] ([IdTracker])
 );

Tracker position is used to store positions send by car trackers. So I have a lot of insert going on. And I often need to get the last position known for a tracker.

So here is a query generated by Entity Framework :

SELECT 
    [Limit1].[IdTrackerPosition] AS [IdTrackerPosition], 
    [Limit1].[TrackerId] AS [TrackerId], 
    [Limit1].[Position] AS [Position], 
    [Limit1].[Date] AS [Date], 
    [Limit1].[Speed] AS [Speed], 
    [Limit1].[NbSatellites] AS [NbSatellites], 
    [Limit1].[Direction] AS [Direction], 
    [Limit1].[HDOP] AS [HDOP]
    FROM   (SELECT DISTINCT 
        [Extent1].[TrackerId] AS [TrackerId]
        FROM [dbo].[TrackerPositions] AS [Extent1]
        WHERE ([Extent1].[Position] IS NOT NULL) AND ([Extent1].[TrackerId] IN (1, 48)) ) AS [Distinct1]
    OUTER APPLY  (SELECT TOP (1) [Project2].[IdTrackerPosition] AS [IdTrackerPosition], [Project2].[TrackerId] AS [TrackerId], [Project2].[Position] AS [Position], [Project2].[Date] AS [Date], [Project2].[Speed] AS [Speed], [Project2].[NbSatellites] AS [NbSatellites], [Project2].[Direction] AS [Direction], [Project2].[HDOP] AS [HDOP]
        FROM ( SELECT 
            [Extent2].[IdTrackerPosition] AS [IdTrackerPosition], 
            [Extent2].[TrackerId] AS [TrackerId], 
            [Extent2].[Position] AS [Position], 
            [Extent2].[Date] AS [Date], 
            [Extent2].[Speed] AS [Speed], 
            [Extent2].[NbSatellites] AS [NbSatellites], 
            [Extent2].[Direction] AS [Direction], 
            [Extent2].[HDOP] AS [HDOP]
            FROM [dbo].[TrackerPositions] AS [Extent2]
            WHERE ([Extent2].[Position] IS NOT NULL) AND ([Extent2].[TrackerId] IN (1, 48)) AND ([Distinct1].[TrackerId] = [Extent2].[TrackerId])
        )  AS [Project2]
        ORDER BY [Project2].[IdTrackerPosition] DESC ) AS [Limit1]

And here an index suggested by SQL Server Studio :

CREATE NONCLUSTERED INDEX [_dta_index_TrackerPositions_5_352108395__K2_3] ON [dbo].[TrackerPositions]
(
    [TrackerId] ASC
)
INCLUDE (   [Position]) WITH (SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, ONLINE = OFF) ON [PRIMARY]

Performances are way better with the index, but most of my insert got locked...

Do you guys have any idea about a better index/select I could use ?