networkStream.Read gets incomplete data

[!NoItAll]

So I've been wrapped around the axle on this problem using the tcpClient and networkStream.
My code first sends a byte count (8 bytes) so the receiver knows exactly how much to expect. This works flawlessly. Subsequent transmissions would sometimes get everything, but with large records (I'm sending object(s) serialized as XML) the data would often get truncated.
I tried:

Dim RxSize as Integer = receiveBufferLength(networkStream)
Dim RxBytes(RxSize) as Byte
Do While tcpClient.Available < RxSize
    Threading.Thread.Sleep(100)
End While
 
RxBytes = networkStream.Read(RxBytes, 0, RxSize)
 

But often the tcpClient.Available bytes was less than the RxSize and would NOT increment to the expected RxSize.

What I found is that once the tcpClient.Available bytes stopped incrementing I had go get them and then the underlying socket would begin adding new bytes to the buffer. A secondary read would get the rest.
I tried setting the tcpClient.ReceiveBufferSize to RxSize - that did not help. I also set tcpClient.NoDelay=True - again no help...
This seemed confusing but here is the code I wound up working out...

' Get the stream
Dim networkStream As NetworkStream = tcpClient.GetStream()
 
'get the buffersize and set it from the data in the first transmission
Dim RxSize As Integer = receiveBufferLength(networkStream)
tcpClient.ReceiveBufferSize = RxSize
 
' Read the stream into a byte array
Dim rxBytes(rxSize) As Byte
 
Dim rxBits(0) As Byte
Dim iBits As Integer = 0
Dim iPos As Integer = 0
 
Dim Timeout As Integer = 0
 
 While iPos < rxSize
    iBits = tcpClient.Available
    ReDim rxBits(iBits)
    networkStream.Read(rxBits, 0, iBits)
    rxBits.CopyTo(rxBytes, iPos)
    iPos += (rxBits.Length - 1)
    Threading.Thread.Sleep(100)
    Timeout += 1
    If Timeout > 20 Then Exit While
 End While
 
 

This does as many reads as necessary to get all of the bytes from the networkStream and concatenates it to my receive buffer (rxBytes). It allows for up to 21 times through the loop before giving up (I don't know if that's enough - but so far its never gone through more than twice)

So my question is:
what do people on this forum think of this approach? Does anyone have an idea for more efficient code?