Thank you Scott
I have switched from FTP to SFTP in response to your suggestion.
Using FTP I tried running a test of uploading two files of approximately 1 Mb in size. The first file was uploading at a speed of approximately 500 bytes/second when my connection with DreamHost spontaneously disconnected after only 4 Kb of the file had been uploaded. I then reconnected and the second file uploaded at about 80 Kb/second. The maximum speed I saw among the fluctuating speeds on the screen during the file uploads was 1000 bytes/second for the first file and 110 Kb/second for the second file. The speeds kept decreasing as the uploads progressed.
Under SFTP I have just tried uploading two files that are just over 7 Mb in size. Both the first and the second file uploaded at about 80 Kb/second. The maximum speeds I saw among the fluctuating speeds on the screen were about 400 Kb/second but they soon dropped to 80 Kb/second and then stayed fairly constant.
I will have to watch over the next few weeks to see if using SFTP does solve the problem. I have noticed in the past that the first file sometimes uploads as fast as the others in situations where I have recently connected to my website with Fetch. I have connected to my website at least a half dozen times with Fetch during the past two days.
If anyone else is considering switching from the default FTP to SFTP then I suggest you read the following two articles in the DreamHost Wiki:
In addition to selecting SFTP in Fetch (my FTP program on a Mac) I discovered that I also had to enter the DreamHost Control Panel and make a preference change in my account to enable SFTP protocol file transfers as explained in the two DreamHost Wiki articles.