Index: sys/netinet/tcp_input.c
===================================================================
--- sys/netinet/tcp_input.c
+++ sys/netinet/tcp_input.c
@@ -523,7 +523,7 @@
 		CC_ALGO(tp)->ecnpkt_handler(tp->ccv);
 
 		if (tp->ccv->flags & CCF_ACKNOW)
-			tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
+			tcp_timer_activate(tp, TT_DELACK, tp->t_delack);
 	}
 }
 
@@ -1995,7 +1995,7 @@
 			 */
 			if (DELAY_ACK(tp, tlen) && tlen != 0)
 				tcp_timer_activate(tp, TT_DELACK,
-				    tcp_delacktime);
+				    tp->t_delack);
 			else
 				tp->t_flags |= TF_ACKNOW;
 
@@ -3059,7 +3059,7 @@
 
 	if (tp->t_flags & TF_DELACK) {
 		tp->t_flags &= ~TF_DELACK;
-		tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
+		tcp_timer_activate(tp, TT_DELACK, tp->t_delack);
 	}
 	INP_WUNLOCK(tp->t_inpcb);
 	return;
Index: sys/netinet/tcp_subr.c
===================================================================
--- sys/netinet/tcp_subr.c
+++ sys/netinet/tcp_subr.c
@@ -401,7 +401,7 @@
 	tcp_rexmit_min = TCPTV_MIN;
 	if (tcp_rexmit_min < 1)
 		tcp_rexmit_min = 1;
-	tcp_rexmit_slop = TCPTV_CPU_VAR;
+	tcp_rexmit_slop = 0;
 	tcp_finwait2_timeout = TCPTV_FINWAIT2_TIMEOUT;
 	tcp_tcbhashsize = hashsize;
 
@@ -828,6 +828,7 @@
 	tp->t_rttvar = ((TCPTV_RTOBASE - TCPTV_SRTTBASE) << TCP_RTTVAR_SHIFT) / 4;
 	tp->t_rttmin = tcp_rexmit_min;
 	tp->t_rxtcur = TCPTV_RTOBASE;
+	tp->t_delack = tcp_delacktime;
 	tp->snd_cwnd = TCP_MAXWIN << TCP_MAX_WINSHIFT;
 	tp->snd_ssthresh = TCP_MAXWIN << TCP_MAX_WINSHIFT;
 	tp->t_rcvtime = ticks;
Index: sys/netinet/tcp_timer.h
===================================================================
--- sys/netinet/tcp_timer.h
+++ sys/netinet/tcp_timer.h
@@ -75,7 +75,7 @@
 #define	TCPTV_MSL	( 30*hz)		/* max seg lifetime (hah!) */
 #define	TCPTV_SRTTBASE	0			/* base roundtrip time;
 						   if 0, no idea yet */
-#define	TCPTV_RTOBASE	(  3*hz)		/* assumed RTO if no info */
+#define	TCPTV_RTOBASE	( hz )			/* assumed RTO if no info - RFC 6298 */
 
 #define	TCPTV_PERSMIN	(  5*hz)		/* retransmit persistence */
 #define	TCPTV_PERSMAX	( 60*hz)		/* maximum persist interval */
@@ -107,7 +107,7 @@
  * The prior minimum of 1*hz (1 second) badly breaks throughput on any
  * networks faster then a modem that has minor (e.g. 1%) packet loss.
  */
-#define	TCPTV_MIN	( hz/33 )		/* minimum allowable value */
+#define	TCPTV_MIN	( 3 )			/* minimum allowable value - see above */
 #define TCPTV_CPU_VAR	( hz/5 )		/* cpu variance allowed (200ms) */
 #define	TCPTV_REXMTMAX	( 64*hz)		/* max allowable REXMT value */
 
@@ -117,7 +117,7 @@
 
 #define	TCP_MAXRXTSHIFT	12			/* maximum retransmits */
 
-#define	TCPTV_DELACK	( hz/10 )		/* 100ms timeout */
+#define	TCPTV_DELACK	( hz/25 )		/* 40ms timeout */
 
 #ifdef	TCPTIMERS
 static const char *tcptimers[] =
Index: sys/netinet/tcp_timer.c
===================================================================
--- sys/netinet/tcp_timer.c
+++ sys/netinet/tcp_timer.c
@@ -649,6 +649,8 @@
 		rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
 	TCPT_RANGESET(tp->t_rxtcur, rexmt,
 		      tp->t_rttmin, TCPTV_REXMTMAX);
+	/*  1 < delack < tcp_delacktime - and should scale down with RTO/2 */
+	TCPT_RANGESET(tp->t_delack, (rexmt >> 1), 1, tcp_delacktime);
 
 	/*
 	 * We enter the path for PLMTUD if connection is established or, if
Index: sys/netinet/tcp_var.h
===================================================================
--- sys/netinet/tcp_var.h
+++ sys/netinet/tcp_var.h
@@ -206,6 +206,7 @@
 	u_int	t_tsomaxsegsize;	/* TSO maximum segment size in bytes */
 	u_int	t_pmtud_saved_maxopd;	/* pre-blackhole MSS */
 	u_int	t_flags2;		/* More tcpcb flags storage */
+	u_int	t_delack;		/* delayed ack timer */
 
 	uint32_t t_ispare[8];		/* 5 UTO, 3 TBD */
 	void	*t_pspare2[4];		/* 1 TCP_SIGNATURE, 3 TBD */