PostgreSQL - fetch the rows which have the Max value for a column in each GROUP BY group

I'm dealing with a Postgres table (called "lives") that contains records with columns for time_stamp, usr_id, transaction_id, and lives_remaining. I need a query that will give me the most recent lives_remaining total for each usr_id

1. There are multiple users (distinct usr_id's)
   
2. time_stamp is not a unique identifier: sometimes user events (one by row in the table) will occur with the same time_stamp.
   
3. trans_id is unique only for very small time ranges: over time it repeats
   
4. remaining_lives (for a given user) can both increase and decrease over time

example:

time_stamp|lives_remaining|usr_id|trans_id
-----------------------------------------
  07:00  |       1       |   1  |   1    
  09:00  |       4       |   2  |   2    
  10:00  |       2       |   3  |   3    
  10:00  |       1       |   2  |   4    
  11:00  |       4       |   1  |   5    
  11:00  |       3       |   1  |   6    
  13:00  |       3       |   3  |   1    

As I will need to access other columns of the row with the latest data for each given usr_id, I need a query that gives a result like this:

time_stamp|lives_remaining|usr_id|trans_id
-----------------------------------------
  11:00  |       3       |   1  |   6    
  10:00  |       1       |   2  |   4    
  13:00  |       3       |   3  |   1    

As mentioned, each usr_id can gain or lose lives, and sometimes these timestamped events occur so close together that they have the same timestamp! Therefore this query won't work:

SELECT b.time_stamp,b.lives_remaining,b.usr_id,b.trans_id FROM 
      (SELECT usr_id, max(time_stamp) AS max_timestamp 
       FROM lives GROUP BY usr_id ORDER BY usr_id) a 
JOIN lives b ON a.max_timestamp = b.time_stamp

Instead, I need to use both time_stamp (first) and trans_id (second) to identify the correct row. I also then need to pass that information from the subquer